Position assistance information in TN / NTN scenario

Abstract

Systems and methods are disclosed that relate to position assistance information in a Terrestrial Network (TN) cell that is used to obtain a position estimate of a User Equipment (UE) for use when performing an action(s) with respect to an Non-Terrestrial Network (NTN) cell(s). In one embodiment, a method performed by a UE for obtaining an estimate of a position of the UE in a cellular communications system comprises receiving position assistance information from a TN node on a TN cell and obtaining a position of the UE based on the position assistance information. The method further comprises performing one or more actions with respect to one or more NTN cells, based on the position of the UE obtained based on the position assistance information. In this manner, the UE is enabled to obtain a valid position estimate which can be used to perform action(s) on NTN cell(s) without delay.

Description

POSITION ASSISTANCE INFORMA TION IN TN / NTN SCENARIOTechnical Field

[0001] The present disclosure relates to a cellular communications system including both Terrestrial Network (TN) cells and Non-Terrestrial Network (NTN) cells and, more specifically, positioning of User Equipments (UEs) in such a system.Background

[0002] There is an ongoing resurgence of satellite communications. Several plans for satellite networks have been announced in the past few years. The target services vary, from backhaul and fixed wireless, to transportation, to outdoor mobile, to Internet of Things (loT). Satellite networks could complement mobile networks on the ground by providing connectivity to underserved areas and multicast / broadcast services.

[0003] To benefit from the strong mobile ecosystem and economy of scale, adapting the terrestrial wireless access technologies including 3rdGeneration Partnership Project (3GPP) Long Term Evolution (LTE) and New Radio (NR) for satellite networks is drawing significant interest, which has been reflected in the 3GPP standardization work. In 3GPP Release 15, 3GPP started the work to prepare NR for operation in a Non-Terrestrial Network (NTN). The work was performed within the study item "NR to support NonTerrestrial Networks" and resulted in 3GPP Technical Report (TR) 38.811. In 3GPP Release 16, the work to prepare NR for operation in an NTN network continued with the study item "Solutions for NR to support Non-Terrestrial Network", which has been captured in 3GPP TR 38.821. In parallel. The interest to adapt Narrowband Internet of Things (NB-IoT) and LTE for Machine Type Communications (LTE-M) for operation in NTN is growing. As a consequence, 3GPP release 17 contains both a work item on NR NTN (see RP-193234) and a study item and work item on NB-IoT and LTE-M support for NTN (see RP-211601).

[0004] In the work on 3GPP release 18, a topic that is relevant to the present disclosure is enhancements of Terrestrial Network (TN)-NTN mobility.

[0005] A satellite radio access network usually includes the following components:- a satellite that refers to a space-borne platform;- an earth-based gateway that connects the satellite to a base station or a core network, depending on the choice of architecture;- a feeder link that refers to the link between a gateway and a satellite; and- an access link, or service link, that refers to the link between a satellite and a User Equipment (UE).

[0006] Depending on the orbit altitude, a satellite may be categorized as a Low Earth Orbit (LEO) satellite, a Medium Earth Orbit (MEO) satellite, or a Geostationary Earth Orbit (GEO) satellite. Typical heights for a LEO satellite range from 250 to 1,500 kilometers (km), with orbital periods ranging from 90 to 120 minutes. Typical heights for a MEO satellite range from 1,500 to 35,786 km, with orbital periods (PMEO) in the range of: 2 hours < PMEO < 24 hours. MEO and LEO satellites are also known as NonGeo Synchronous Orbit (NGSO) type of satellites. A typical height of a GEO satellite is about 35,786 km, with an orbital period of 24 hours. A GEO satellite is also known as a Geo Synchronous Orbit (GSO) type of satellite.

[0007] Two basic architectures can be distinguished for satellite communication networks, depending on the functionality of the satellites in the system. These two architectures are:- Transparent Payload (also referred to as bent pipe architecture): In the transparent payload architecture, the satellite forwards the received signal between the terminal (e.g., UE) and the network equipment on the ground with only amplification and a shift from uplink frequency to downlink frequency. When applied to the 3GPP NR architecture and terminology, the transparent payload architecture means that the gNodeB (gNB) is located on the ground, and the satellite forwards signals / data between the gNB and the UE.- Regenerative Payload: In the regenerative payload architecture, the satellite includes on-board processing to demodulate and decode the received signal and regenerate the signal before sending it back to the earth. When applied to the 3GPP NR architecture and terminology, the regenerative payload architecture means that the gNB is located in the satellite.In the work item for NR NTN in 3GPP Release 17, only the transparent payload architecture is considered.

[0008] Figure 1 shows an example architecture of a satellite network with bent pipe transponders (i.e., the transparent payload architecture). The base station (i.e., the gNB in the case of NR) may be integrated in the gateway or connected to the gateway via a terrestrial connection (e.g., a wire, optic fiber, or wireless link).

[0009] The significant orbit height of the satellite means that satellite communication networks are characterized by a path loss that is significantly higher than what is expected in terrestrial networks. To overcome the pathloss, it is often required that the access and feeder links are operated in line-of-sight conditions and that the UE is equipped with an antenna offering high beam directivity.

[0010] A communication satellite typically generates several beams over a given geographic area. The footprint of a beam is usually in an elliptic shape, which has been traditionally considered as a cell, but a cell consisting of multiple beams is not precluded. The footprint of a beam is also often referred to as a spotbeam. The spotbeam may move over the Earth's surface with the satellite movement and the Earth's rotation or may be Earth-fixed with some beam pointing mechanism used by the satellite to compensate for its motion. The size of a spotbeam depends on the system design and may range from tens of kilometers to a few thousands of kilometers.

[0011] In comparison to the beams observed in a terrestrial network, the satellite, or NTN, beam may provide a very wide footprint and may cover an area outside of the area defined by the served cell. A beam covering adjacent cells will overlap with the adjacent cells and cause significant levels of intercell interference, resulting from the slow decrease of the signal strength in the outwards radial direction. This is due in part to the high elevation angle and long distance to the network-side (satellite-borne) transceiver, which, compared with terrestrial cells, results in a comparatively small relative difference between the distance from the cell center to the satellite and the distance from a point at the cell edge to the satellite. To overcome the large levels of interference, a typical approach in NTN is to configure different cells with different carrier frequencies and polarization modes.

[0012] Three types of beams or cells are supported in NTN, namely:- Earth-fixed beams / cells: provisioned by beam(s) continuously covering the same geographical areas all the time (e.g., in the case of GEO satellites);- Quasi-earth-fixed beams / cells: provisioned by beam(s) covering one geographic area for a limited period and a different geographic area during another period (e.g., in the case of NGSO satellites generating steerable beams); and- Earth-moving beams / cells: provisioned by beam(s) whose coverage area slides over the earth surface (e.g., in the case of NGSO satellites generating fixed or non-steerable beams).Throughout the present disclosure, the description hereafter uses the terms "beam" and "cell" interchangeably, unless explicitly noted otherwise. Of the three above cell types, quasi-earth-fixed cells and moving cells seem to be the ones most promising for actual deployment. In the case of moving cells, each cell (the footprint of its beam(s)) moves across the surface of the earth as its serving satellite moves along its orbit.

[0013] In the case of quasi-earth-fixed cells, the cell area (as the name implies) remains fixed to the same geographical area, regardless of satellite movements. To enable this, a serving satellite has a means for dynamically directing its beam(s) so that the same area of the earth is covered despite the satellite's movement. However, since the satellites orbit around the earth, the same satellite will only be able to cover the same area on the earth for a limited time, unless the satellite is in a geostationary orbit (and note that LEO satellites have the most traction in the satellite communication industry). This means that different satellites will have the task of covering a certain geographical cell area at different time periods. When this task is switched from one satellite to another, this in principle means that one cell is replaced by another, although covering the same area (often referred to as a cell switch). As a consequence, all UEs connected in the old cell (e.g., NR UEs in Radio Resource Control (RRC) Connected (RRC_CONNECTED) state) have to be handed over (or otherwise moved, e.g. using RRC connection reestablishment) from the old to the new cell, and all UEs camping on the old cell (i.e., UEs in RRC Idle (RRC_IDLE) or RRC Inactive (RRC_INACTIVE) state) have to perform cell reselection to the new cell.

[0014] A similar situation occurs in conjunction with feeder link switches, i.e., when the serving satellite remains the same but its connection to the ground changes from one (old) gateway (GW) / gNB to another (new) GW / gNB. A similar situation also occurs in this case where there is switch between an old cell and a new cell (i.e., the old cell is replaced by a new cell).

[0015] In terms of such cell switches, there are two alternative principles: (1) hard switch and (2) soft switch. With hard switch, there is an instantaneous switch from the old cell to the new cell, i.e., the new cell appears at the same time as the old cell disappears. This makes completely seamless (i.e., interruption free) handover in practice impossible and creates a situation which may lead to overload of the access resources in the new cell, due to potential access attempt peaks when many UEs try to access the new cell right after the cell switch. With soft switch there is a time periodduring which the new and the old cell coexist (i.e., overlap), covering the same geographical area. This coexistence / overlap period allows some time for connected UEs to be handed over and for camping UEs to reselect to the new cell, which facilitates distribution of the access load in the new cell and thereby also provides better conditions for handovers with shorter interruption time. Soft switch is likely to be the most prevalent cell switch principle in quasi-earth-fixed cell deployments.

[0016] Ephemeris data (sometimes referred to as "ephemeris information" or "ephemeris parameters" or just "ephemeris") is data that allows a UE (or other entity) to determine a satellite's position and velocity, i.e., the ephemeris data contains parameters related to the satellite's orbit. There are several different formats defined for ephemeris data.

[0017] In 3GPP TR 38.821, it has been captured that ephemeris data should be provided to the UE, for example, to assist with pointing a directional antenna (or an antenna beam) towards the satellite and to calculate a correct Timing Advance (TA) and Doppler shift. In NR NTN and loT NTN, ephemeris data will be broadcast in the system information (SI) in each cell, included in an NTN specific System Information Block (SIB) named SIB19 in NR NTN and SIB31 in loT NTN.

[0018] A satellite orbit can be fully described using six parameters. Exactly which set of parameters is chosen can be decided by the user. Many different representations are possible. For example, a choice of parameters used often in astronomy is the set (a, £, I, Q, co, t). Here, the semi-major axis a and the eccentricity £ describe the shape and size of the orbit ellipse; the inclination i, the right ascension of the ascending node Q, and the argument of periapsis co determine its position in space; and the epoch time t determines a reference time (e.g., the time when the satellites moves through periapsis). This set of parameters included in one example ephemeris data format is illustrated in Figure 2.

[0019] As an example of a different parametrization, the Two-Line Elements (TLEs) use mean motion n and mean anomaly M instead of a and t. A completely different set of parameters is the position and velocity vector (x, y, z, vx, vy, vz) of a satellite. These are sometimes called orbital state vectors. They can be derived from the orbital elements and vice versa, since the information they contain is equivalent. All these formats (and many others) are possible choices for the format of ephemeris data to be used in an NTN.

[0020] An aspect discussed during the 3GPP study item and captured in 3GPP TR 38.821 is the validity time of ephemeris data. Predictions of satellite positions in general degrade with increasing age of the ephemeris data used, due to atmospheric drag, maneuvering of the satellite, imperfections in the orbital models used, etc. Therefore, the publicly available TLE data are updated quite frequently. For example, the update frequency depends on the satellite and its orbit and ranges from weekly to multiple times a day for satellites on very low orbits which are exposed to strong atmospheric drag and need to perform correctional maneuvers often. Even more frequent updates will be used in NR NTN (and loT NTN) to allow the UE to determine / predict the satellite's position (and velocity) accurately enough to satisfy the requirements in NTN, e.g., to enable a UE to calculate an accurate enough UE-specific TA.

[0021] In 3GPP Release 17, it is assumed, for both NR NTN and loT NTN, that every UE is equipped with a Global Navigation Satellite System (GNSS) receiver. A GNSS comprises a set of satellites orbiting the earth in orbits crossing each other, such that the orbits are distributed around the globe. The satellites transmit signals and data that allows a receiving device on earth to accurately determine time and frequency references and, maybe most importantly, accurately determine its position, provided that signals are received from a sufficient number of satellites (e.g., four). The position accuracy may typically be in the range of a few meters, but using averaging over multiple measurements, a stationary device may achieve much better accuracy.

[0022] A well-known example of a GNSS is the American Global Positioning System (GPS). Other examples are the Russian Global Navigation Satellite System (GLONASS), the Chinese BeiDou Navigation Satellite System, and the European Galileo.

[0023] The transmissions from GNSS satellites include signals that a receiving device uses to determine the distance to the satellite. By receiving such signals from multiple satellites, the device can determine its position. However, this requires that the device also knows the positions of the satellites. To enable this, the GNSS satellites also transmit data about their own orbits from which position at a certain time can be derived. In GPS, such information is referred to as ephemeris data and almanac data (or sometimes lumped together under the term navigation information).

[0024] The time required to perform a GNSS measurement, e.g. GPS measurement, may vary widely, depending on the circumstances, mainly depending on the status of the ephemeris and almanac data the measuring devices has previously acquired, if any.In the worst case, a GPS measurement can take several minutes. GPS uses a bit rate of 50 bits per second (bps) for transmitting its navigation information. The transmission of the GPS date, time, and ephemeris information takes 90 seconds. Acquiring the GPS almanac containing orbital information for all satellites in the GPS constellation takes more than 10 minutes. If a UE already possesses this information, the synchronization to the GPS signal for acquiring the UE position and Coordinated Universal Time (UTC) is significantly faster. The state of a GNSS receiver with regards to the above may be classified as cold, warm, or hot state, where the time required to perform a GNSS measurement to determine a position is the longest in cold state and the shortest in hot state. These states can be more specifically described as follows:• Hot state: The device remembers its last calculated position and the satellites in view, the almanac used, and the UTC Time. It leverages this information to makes an attempt to lock onto the same satellites and calculate a new position. This is the quickest state but, generally, it only works close to the location of the last GNSS measurement.• Warm state: The device remembers its last calculated position, almanac used, and UTC Time, but not which satellites were in view. It then performs a reset and attempts to obtain the satellite signals and calculates a new position. The receiver has a general idea of which satellites to look for because it knows its last position and the almanac data helps identify which satellites are visible in the sky.• Cold state: The device does not have any usable previous information. The device attempts to locate satellites, download the almanac, and calculate the new location. This takes the longest time of all.

[0025] A relevant note on terminology is that a position determined based on a GNSS measurement, or the act of determining a position based on a GNSS measurement, is also referred to as a "position fix".

[0026] In 3GPP Release 17, it is assumed, for both NR NTN and loT NTN, that every UE is equipped with a GNSS receiver, capable of determining its own location using GNSS measurements, and, based on that, handles timing and frequency synchronization. The GNSS receiver allows a device to estimate its geographical position. In one example, an NTN gNB carried by a satellite, or communicating via a satellite, broadcasts its ephemeris data (i.e., data that informs the UE about thesatellite's position, velocity, and orbit) and full or partial feeder link delay in the form of so-called common TA parameters to a GNSS equipped UE. The UE can then determine the propagation delay, the delay variation rate, the Doppler shift, and its variation rate based on the UE's own location (obtained through GNSS measurements) and the satellite location and movement (derived from the ephemeris data). The UE may use this knowledge to compensate its uplink transmissions for the propagation delay and Doppler effect. In particular, the UE uses knowledge of its location and broadcast information about the satellite's position (i.e., ephemeris data) to calculate the UE- satellite Round-Trip Time (RTT), which is then used in UE autonomous calculation of a Timing Advance (TA). However, an loT NTN UE is not expected to be able to perform a GNSS measurement while receiving transmissions from network at the same time.

[0027] The GNSS receiver also allows a device to determine a time reference (e.g., in terms of Coordinated Universal Time (UTC)) and frequency reference, which may facilitate the UE's handling of the timing and frequency synchronization in an NR or LTE based NTN.

[0028] The 3GPP release 17 study item description (SID) on NB-IoT and LTE-M for NTN supports this observation:GNSS capability in the UE is taken as a working assumption in this study for both NB-IoT and eMTC devices. With this assumption, UE can estimate and pre-compensate timing and frequency offset with sufficient accuracy for UL transmission. Simultaneous GNSS and NTN NB-IoT / eMTC operation is not assumed.

[0029] When using GNSS measurements for purposes related to the operation and performance of an NR NTN or loT NTN, the GNSS measurement must be fresh enough to be reliable. For this reason, the notion of a GNSS validity timer (or validity duration) has been introduced, which governs the maximum age UE location information may have when used in such operations (e.g., for calculation of a timing advance). A suitable value for this maximum age may depend on the UE's implementation, and therefore the GNSS validity timer is a UE implementation specific mechanism. However, the standard specifications for loT NTN include means by which the UE can inform the network (e.g., the serving base station) of the remaining time of the UE's currently running GNSS validity timer.

[0030] Propagation delay or RTT is an important aspect of satellite communication since long propagation delay / RTT has consequences on the timing advance. Theexpected impacts of the propagation delay in an NTN is different from the impacts of the propagation delay in a terrestrial mobile system. For a bent pipe satellite network, the UE-gNB round-trip delay may, depending on the orbit height of the satellite, range from a few or tens of milliseconds in the case of LEO satellites to several hundreds of milliseconds for GEO satellites. As a comparison, the round-trip delays in terrestrial cellular networks are typically below 1 ms.

[0031] The distance between the UE and a satellite can vary significantly, depending on the position of the satellite and thus the elevation angle £ seen by the UE. Assuming circular orbits, the minimum distance is realized when the satellite is directly above the UE (£ = 90°), and the maximum distance when the satellite is at the smallest possible elevation angle. Table 1 shows the distances between the satellite and UE for different orbital heights and elevation angles together with the one-way propagation delay and the maximum propagation delay difference (the difference from the propagation delay at £ = 90°). Note that this table assumes the regenerative payload architecture. For the transparent payload case, the propagation delay between gateway and satellite needs to be considered as well, unless the base station corrects for that.Table 1: Propagation delay for different orbital heights and elevation angles.

[0032] The propagation delay may also be highly variable due to the high velocity of the LEO and MEO satellites and change in the order of 10 - 100 microseconds (ps) every second, depending on the orbit altitude and satellite velocity.

[0033] The long propagation delays in NTN have many consequences, one of which being that large TA values have to be used, where a TA is the time a UE has to advance its uplink (UL) transmission in relation to the corresponding frame, slot, and symbol in the downlink (DL) to achieve alignment between the UL and DL frame / slot / symbol structures at an ULVDL alignment reference point, which typically is the gNB in the case of NR. In addition, due to the fast movement of the satellite (excluding GEO satellites), the TA will continuously change and will do so quite rapidly. 3GPP has dealt with these circumstances through a combination of new parameters and introduction of the principle of UE autonomous adaptation of the TA.

[0034] Typically, the network wants the UL and DL to be aligned at the gNB receiver, which means that the TA should be equal to the UE-gNB RTT. The UE-gNB RTT can be divided into two parts: the UE-satellite RTT (i.e., the service link RTT) and the gNB- satellite RTT (which is equal to the feeder link RTT assuming that the GW and the gNB are collocated). The satellite-gNB RTT is equal for all locations in the cell and thus the same for all UEs in the cell, whereas the UE-satellite RTT depends on the UE's location and thus is UE specific.

[0035] To take care of the part of the TA that is common for all UEs in the cell, the satellite broadcasts, in the system information in a new SIB with NTN specific data (SIB19 in NR NTN and SIB31 in loT NTN), so-called Common TA information, consisting of a Common TA value, the first time derivative of the Common TA value (denoted as "drift"), and the second time derivative of the Common TA value (denoted as "drift variation"). The UE specific part of the TA, i.e., the UE-satellite RTT is left to the UE to autonomously calculate. To do this, the UE obtains its own location and the satellite position. The UE obtains its own location e.g., using GNSS measurements, and the UE derives the satellite's position (as well as its velocity) from the ephemeris data broadcast by the gNB in the same SIB as the Common TA parameters. The ephemeris data and the Common TA parameters are nominally valid at a so-called epoch time, which is also indicated in the same SIB. If the epoch time indication is absent in the SIB, the epoch time is assumed to be the end of the System Information (SI) window in which the SIB was received. Based on the ephemeris data, the UE can predict thesatellite's position a certain time into the future, and the first and second time derivatives (i.e., the drift and drift variation parameters) of the Common TA allows the UE to calculate how the Common TA value changes with time. Furthermore, the broadcast ephemeris data and Common TA parameters have a limited validity time, which is also indicated in the same SIB. The ephemeris data and Common TA parameters the UE uses when calculating the UE specific TA have to be valid, i.e., their validity time must not have expired. The same goes for the UE location information, typically based on a GNSS measurement, the UE uses in the TA calculation, in particular to calculate the UE-satellite RTT.

[0036] 3GPP has also introduced support for the possibility to place the UL / DL alignment reference point at some other place than in the gNB. This support comes in the form of a parameter denoted as Kmac (also referred to as K_mac). The Kmac parameter takes care of the RTT between the gNB and the chosen UL / DL alignment reference point. Hence, Kmac = 0 means that the UL / DL alignment reference point is located in the gNB, while other Kmac values will place the UL / DL alignment reference point somewhere between the gNB and the satellite. Kmac is included in the same SIB as the other above mentioned NTN specific configuration parameters. Broadcast of Kmac is optional and absence of a Kmac parameter in the concerned SIB implicitly means that Kmac = 0 should be used.

[0037] When calculating the UE specific TA, the UE only uses the Common TA parameters, the ephemeris data, and its own location, i.e., Kmac is not needed for this calculation. However, the UE needs to know Kmac for other purposes, e.g., so that it can adapt certain timers to the UE-gNB RTT.

[0038] For NTNs using 3GPP technology, in particular 5G / NR, the long propagation delay means that the TA the UE uses for its uplink transmissions is essential and has to be much greater than in terrestrial networks in order for the uplink and downlink to be time-aligned at the gNB (or at another point if Kmac > 0), as is the case in NR and LTE. One of the purposes of the Random Access (RA) procedure is to provide the UE with a valid TA. However, even the random access preamble (i.e. the initial message from the UE in the random access procedure) has to be transmitted with a timing advance to allow a reasonable size of the RA preamble reception window in the gNB and to ensure that the cyclic shift of the preamble's Zadoff-Chu sequence cannot be so large that it makes the Zadoff-Chu sequence, and thus the preamble, appear as another Zadoff Chusequence, and thus another preamble, based on the same Zadoff-Chu root sequence. However, the TA used for RA does not have to be as accurate as the TA the UE subsequently uses for other uplink transmissions, where the latter TA has to be accurate enough to keep the timing error smaller than the cyclic prefix (CP).

[0039] In conjunction with the random access procedure, the gNB provides the UE with an accurate (i.e., fine-adjusted) TA in the Random Access Response (RAR) message in the case of 4-step RA or in MsgB in the case of 2-step RA, based on the time of reception of the random access preamble. In terrestrial NR, the gNB can subsequently adjust the UE's TA using a Timing Advance Command Medium Access Control (MAC) Control Element (CE) or an Absolute Timing Advance Command MAC CE, based on the timing of receptions of uplink transmissions from the UE. A goal with such network control of the UE's timing advance is typically to keep the time error of the UE's uplink transmissions at the gNB's receiver within the cyclic prefix, which is required for correct decoding of the uplink transmissions, e.g., on the Physical Uplink Shared Channel (PUSCH) and the Physical Uplink Control Channel (PUCCH).

[0040] The timing advance control framework for terrestrial NR and LTE also includes a time alignment timer with which the gNB configures the UE. The time alignment timer is restarted every time the gNB adjusts the UE's TA and, if the time alignment timer expires, the UE is not allowed to transmit in the uplink without a prior random access procedure, which serves the purpose of providing the UE with a valid timing advance. These rules associated with the time alignment timer will be the same in NTN, but the relation and / or interaction between the time alignment timer and certain NTN specific functionality, e.g., related to GNSS measurements, may impact the role of the time alignment timer in NTN. For NTN, 3GPP has also agreed that in addition to the gNB's control of the UE's TA, the UE is allowed to autonomously update its TA based on estimation of changes in the UE-gNB RTT using the UE's location and broadcast parameters related to the satellite orbit and the feeder link RTT, as previously described.

[0041] The long propagation delays and the resulting large TA that a UE has to use in an NTN also impacts the scheduling of uplink transmissions. Specifically, the network has to take the large TA into account when it determines the delay to be used between an UL grant (i.e., a Downlink Control Information (DCI) on the Physical Downlink Control Channel (PDCCH) allocating uplink transmission resources for the UE to transmiton) and the uplink transmission resources the UL grant allocates. For this purpose, a new parameter denoted as "Kofrset" (or "Koffset" or "K_offset") is introduced, which is added to the legacy delay, e.g., added to the legacy delay parameter K2 (or K2) contained in the UL grant in NR NTN. The Kofrset parameter comes in two forms: the cellspecific Koffset, which is broadcast in the system information and which is common for all UEs in the cell, and the UE-specific Koffset, which the network optionally configures for each UE. Note that configuration of a UE-specific Koffset value is optional, and when it is absent, the cell-specific Koffset value applies. To facilitate for the network to determine a suitable UE-specific Koffset value for a certain UE, a mechanism for TA reporting is introduced in NTN, whereby the UE can report its current TA to the network (where the granularity of the reported TA value is one slot).

[0042] As discussed above, due to the special operating conditions in a NonTerrestrial Network, the system information broadcast in an NTN cell has to include NTN-specific information. To serve this purpose, a new SIB (SIB19) is introduced in NR NTN which contains NTN-specific information. In loT NTN, the new SIB31 more or less corresponds to SIB19 in NR NTN.

[0043] In 3GPP TS 38.331 version 17.5.0, SIB19 is defined in the ASN.l code of Figures 3A and 3B. Furthermore, the NTN-Config-rl7 Information Element (IE) is defined as shown in Figures 4A, 4B and 4C in ASN.l code in the same specification. The Ephemerisinfo IE is defined as shown in Figures 5A and 5B in ASN.l code in the same specification.

[0044] The NTN described above is based on 5G / NR technology adapted for communication via satellites. But an NTN standard for loT, denoted as "loT NTN", is also being specified in Release 17 of the 3GPP standards. loT NTN is based on the LTE NB-IoT technology adapted for communication via satellites. To distinguish NTN based 5G / NR technology from loT NTN, NTN based on 5G / NR technology is often referred to as "NR NTN". In light of these distinctions, depending on the context, the term "NTN" is sometimes used herein to refer to either or both of NR NTN and loT NTN, and sometimes the term "NTN" is used to refer only to NR NTN.

[0045] One important difference between NR NTN and loT NTN is that while an NR NTN UE is expected to be able to perform GNSS measurements independently of its communication in the NTN (e.g., using separate receiver circuitry for the two operations), an loT NTN is not expected to be able to do that. Hence, to ensure thatdata is not lost in the loT NTN while the UE performs a GNSS measurement, the network has the option to configure a GNSS measurement gap for a UE, during which the UE can perform a GNSS measurement. A measurement gap is a time period during which the network refrains from scheduling any downlink or uplink transmissions for the UE.

[0046] A terrestrial network (TN) comprises of one or more radio network nodes (e.g., base stations) deployed on the ground. The TN may also be referred to as a non- NTN network, non-satellite network, or the like. A UE operating in a TN is served by a radio network node belonging to the TN.

[0047] The TN is traditionally deployed using fixed base stations, which do not move. Therefore, the fixed base station is statically deployed in a certain location within the coverage area. However, the TN may also comprise of one or more movable radio network nodes (e.g., mobile base stations such as drones, high altitude platform station (HAPS), etc.) which can move from one location to another.Summary

[0048] Systems and methods are disclosed that relate to position assistance information in a Terrestrial Network (TN) cell that is used to obtain a position estimate of a User Equipment (UE) for use when performing one or more actions with respect to one or more Non-Terrestrial Network (NTN) cells. In one embodiment, a method performed by a UE for obtaining an estimate of a position of the UE in a cellular communications system comprises receiving position assistance information from a TN node on a TN cell and obtaining a position of the UE based on the position assistance information. The method further comprises performing one or more actions with respect to one or more NTN cells, based on the position of the UE obtained based on the position assistance information. In this manner, the UE is enabled to obtain a valid position estimate which can be used to perform action(s) (e.g., setup uplink synchronization and perform measurements) on NTN cell(s) without delay.

[0049] In one embodiment, the one or more actions comprise performing measurements on the one or more NTN cells, based on the position of the UE obtained based on the position assistance information.

[0050] In one embodiment, the one or more actions comprise performing uplink synchronization with respect to a NTN cell from among the one or more NTN cells, based on the position of the UE obtained based on the position assistance information.

[0051] In one embodiment, the position obtained based on the position assistance information is used to perform the one or more actions in place of a position of the UE obtained via a Global Navigation Satellite System (GNSS) receiver.

[0052] In one embodiment, receiving the position assistance information comprises receiving broadcast information comprising the position assistance information on the TN cell.

[0053] In one embodiment, receiving the position assistance information comprises receiving the position assistance information via one or more dedicated messages.

[0054] In one embodiment, the UE is located at a position that is served by both the TN cell and at least one of the one or more NTN cells.

[0055] In one embodiment, the position assistance information comprises position assistance information for the TN cell.

[0056] In one embodiment, the position assistance information comprises position assistance information for the TN cell and position assistance information for one or more additional TN cells. In one embodiment, obtaining the position of the UE based on the position assistance information comprises obtaining the position of the UE based on the position assistance information for the TN cell and the position assistance information for one or more additional TN cells.

[0057] In one embodiment, the position assistance information comprises a position of an antenna which the TN node uses for downlink transmissions and uplink receptions in the TN cell, and obtaining the position of the UE based on the position assistance information comprises using the position of the antenna which the TN node uses for downlink transmissions and uplink receptions in the TN cell as the position of the UE.

[0058] In one embodiment, the position assistance information comprises information that provides a mapping between a plurality of Synchronization Signal (SS) I Physical Broadcast Channel (PBCH) Block (SSB) beams and a respectively plurality of geographical coordinates within a coverage are of the TN cell, and obtaining the position of the UE based on the position assistance information comprises selecting one of the plurality of geographical coordinates that is mapped to one of the SSB beams as the position of the UE. In one embodiment, the selected one of the plurality ofgeographical coordinates is one of the plurality of geographical coordinates that is mapped to one of the plurality of SSB beams that satisfies a predefined criterion. In one embodiment, the predefined criterion is a criterion that the one of the plurality of SSB beams is the one having a highest Reference Signal Received Power, RSRP, at the UE.

[0059] In one embodiment, the position assistance information comprises a position of an antenna which the TN node uses for downlink transmissions and uplink receptions in the TN cell that is common for a plurality of SSB beams and information that indicates a plurality of beam directions for the plurality of SSB beams, respectively, and obtaining the position of the UE based on the position assistance information comprises computing the position of the UE based on the position of the antenna, one of the plurality of beam directions indicated for one of the plurality of SSB beams in which the UE is located, and a current Timing Advance (TA) of the UE used for uplink transmissions in the TN cell.

[0060] In one embodiment, the position assistance information comprises a position of an antenna which the TN node uses for downlink transmissions and uplink receptions in the TN cell that is common for a plurality of SSB beams, information that indicates a plurality of beam directions for the plurality of SSB beams, respectively, and a round-trip time (RTT) between the antenna and a defined uplink time synchronization reference point for the TN cell. Further, obtaining the position of the UE based on the position assistance information comprises computing the position of the UE based on the position of the antenna, one of the plurality of beam directions indicated for one of the plurality of SSB beams in which the UE is located, a current TA of the UE used for uplink transmissions in the TN cell, and the RTT between the antenna and the defined uplink time synchronization reference point for the TN cell.

[0061] In one embodiment, the position assistance information comprises a position of an antenna which the TN node uses for downlink transmissions and uplink receptions in the TN cell that is common for a plurality of SSB beams and information that indicates a beam direction for at least one of the plurality of SSB beams. Further, obtaining the position of the UE based on the position assistance information comprises computing the position of the UE based on the position of the antenna, a beam direction of one of the plurality of SSB beams in which the UE is located as indicated by or derived from the information that indicates the beam direction for the at least one of the plurality ofSSB beams, and a current TA of the UE used for uplink transmissions in the TN cell. In one embodiment, the UE derives the beam direction of the one of the plurality of SSB beams in which the UE is located based on the information that indicates the beam direction for the at least one of the plurality of SSB beams and a known number of SSB beams used in the TN cell. In one embodiment, the at least one of the plurality of SSB beams for which the position information comprises the information that indicates the beam direction comprises a single SSB beam from among the plurality of SSB beams. In another embodiment, the at least one of the plurality of SSB beams for which the position information comprises the information that indicates the beam direction comprises two SSB beams from among the plurality of SSB beams that are correspond to edge beams of a corresponding sector antenna of the TN node.

[0062] In one embodiment, the position assistance information comprises information that indicates a plurality of positions of a plurality of SSB beams, respectively, and obtaining the position of the UE based on the position assistance information comprises using one of the plurality of positions indicated for one of the plurality of SSB beams in which the UE is located as the position of the UE. In one embodiment, the information that indicates the plurality of positions of the plurality of SSB beams, respectively, comprises, for each SSB beam of the plurality of SSB beams, geographic coordinates that indicate the position of the SSB beam.

[0063] In one embodiment, the position assistance information comprises geographical coordinates of an antenna which the TN node uses for downlink transmissions and uplink receptions in the TN cell that is common for a plurality of SSB beams and geographical coordinates for at least one of the plurality of SSB beams. Further, obtaining the position of the UE based on the position assistance information comprises deriving the position of one of the plurality of SSB beams in which the UE is located from the geographical coordinates of the antenna and the geographical coordinates for the at least one of the plurality of SSB beams.

[0064] In one embodiment, the UE is served by the TN cell.

[0065] In one embodiment, the UE is served by one of the one or more NTN cells.

[0066] In one embodiment, the UE performs the method while in a low activity radio resource control state.

[0067] In one embodiment, the UE performs the method while in a radio resource control connected state.

[0068] Corresponding embodiments of a UE are also disclosed. In one embodiment, a UE for obtaining an estimate of a position of the UE in a cellular communications system is adapted to receive position assistance information from a TN node on a TN cell and obtain a position of the UE based on the position assistance information. The UE is further adapted to perform one or more actions with respect to one or more NTN cells, based on the position of the UE obtained based on the position assistance information.

[0069] In one embodiment, a UE for obtaining an estimate of a position of the UE in a cellular communications system comprises one or more transmitters, one or more receivers, and processing circuitry associated with the one or more transmitters and the one or more receivers. The processing circuitry is configured to cause the UE to receive position assistance information from a TN node on a TN cell and obtain a position of the UE based on the position assistance information. The processing circuitry is further configured to cause the UE to perform one or more actions with respect to one or more NTN cells, based on the position of the UE obtained based on the position assistance information.

[0070] Embodiments of a method performed by a TN node are also disclosed. In one embodiment, a method performed by a TN node comprises providing position assistance information to a UE on a TN cell, wherein the position assistance information comprises information that enables the UE to select or derive a position of the UE.

[0071] In one embodiment, providing the position assistance information to the UE comprises transmitting broadcast information comprising the position assistance information on the TN cell.

[0072] In one embodiment, providing the position assistance information comprises transmitting the position assistance information to the UE via one or more dedicated messages.

[0073] In one embodiment, the UE is located at a position that is served by both the TN cell and at least one NTN cell.

[0074] In one embodiment, the position assistance information comprises position assistance information for the TN cell.

[0075] In one embodiment, the position assistance information comprises position assistance information for the TN cell and position assistance information for one or more additional TN cells.

[0076] In one embodiment, the position assistance information comprises a position of an antenna which the TN node uses for downlink transmissions and uplink receptions in the TN cell.

[0077] In one embodiment, the position assistance information comprises information that provides a mapping between a plurality of SSB beams and a respective plurality of geographical coordinates within a coverage area of the TN cell.

[0078] In one embodiment, the position assistance information comprises a position of an antenna which the TN node uses for downlink transmissions and uplink receptions in the TN cell that is common for a plurality of SSB beams and information that indicates a plurality of beam directions for the plurality of SSB beams, respectively.

[0079] In one embodiment, the position assistance information comprises a position of an antenna which the TN node uses for downlink transmissions and uplink receptions in the TN cell that is common for a plurality of SSB beams, information that indicates a plurality of beam directions for the plurality of SSB beams, respectively, and a RTT between the antenna and a defined uplink time synchronization reference point for the TN cell.

[0080] In one embodiment, the position assistance information comprises a position of an antenna which the TN node uses for downlink transmissions and uplink receptions in the TN cell that is common for a plurality of SSB beams, and information that indicates a beam direction for at least one of the plurality of SSB beams. In one embodiment, the at least one of the plurality of SSB beams for which the position information comprises the information that indicates the beam direction comprises a single SSB beam from among the plurality of SSB beams. In another embodiment, the at least one of the plurality of SSB beams for which the position information comprises the information that indicates the beam direction comprises two SSB beams from among the plurality of SSB beams that are correspond to edge beams of a corresponding sector antenna of the TN node.

[0081] In one embodiment, the position assistance information comprises information that indicates a plurality of positions of a plurality of SSB beams, respectively. In one embodiment, the information that indicates the plurality of positions of the plurality of SSB beams, respectively, comprises, for each SSB beam of the plurality of SSB beams, geographic coordinates that indicate the position of the SSB beam.

[0082] In one embodiment, the position assistance information comprises geographical coordinates of an antenna which the TN node uses for downlink transmissions and uplink receptions in the TN cell that is common for a plurality of SSB beams and geographical coordinates for at least one of the plurality of SSB beams.

[0083] Corresponding embodiments of a TN node are also disclosed. In one embodiment, a TN node is adapted to provide position assistance information to a UE on a TN cell, wherein the position assistance information comprises information that enables the UE to select or derive a position of the UE.

[0084] In another embodiment, a TN node comprises processing circuitry configured to cause the TN node to provide position assistance information to a UE on a TN cell, wherein the position assistance information comprises information that enables the UE to select or derive a position of the UE.Brief Description of the Drawings

[0085] The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

[0086] Figure 1 shows an example architecture of a satellite network with bent pipe transponders (i.e., the transparent payload architecture);

[0087] Figure 2 illustrates a set of parameters included in one example ephemeris data format;

[0088] Figures 3A and 3B illustrates System Information Block (SIB) 9 as defined in 3rdGeneration Partnership Project (3GPP) Technical Specification (TS) 38.331 version 17.5.0;

[0089] Figures 4A, 4B, and 4C illustrate the NTN-Config-rl7 information element as defined in 3GPP TS 38.331 version 17.5.0;

[0090] Figures 5A and 5B illustrates the Ephemerisinfo information element as defined in 3GPP TS 38.331 version 17.5.0;

[0091] Figure 6 illustrates one example of a system in which embodiments of the present disclosure may be implemented;

[0092] Figure 7 is a flow chart that illustrates the operation of the UE and the TN node 606 in accordance with embodiments of the present disclosure;

[0093] Figure 8 is a schematic block diagram of a network node (e.g., a radio network node) according to some embodiments of the present disclosure;

[0094] Figure 9 is a schematic block diagram that illustrates a virtualized embodiment of the radio network node of Figure 8 according to some embodiments of the present disclosure;

[0095] Figure 10 is a schematic block diagram of a UE according to some embodiments of the present disclosure;

[0096] Figure 11 illustrates a telecommunication network connected via an intermediate network to a host computer in accordance with some embodiments of the present disclosure;

[0097] Figure 12 is a generalized block diagram of a host computer communicating via a base station with a UE over a partially wireless connection in accordance with some embodiments of the present disclosure;

[0098] Figure 13 is a flowchart illustrating a method implemented in a communication system in accordance with one embodiment of the present disclosure;

[0099] Figure 14 is a flowchart illustrating a method implemented in a communication system in accordance with one embodiment of the present disclosure;

[0100] Figure 15 is a flowchart illustrating a method implemented in a communication system in accordance with one embodiment of the present disclosure; and

[0101] Figure 16 is a flowchart illustrating a method implemented in a communication system in accordance with one embodiment of the present disclosure.Detailed Description

[0102] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure.

[0103] Note that the description given herein focuses on a 3GPP cellular communications system and, as such, 3GPP terminology or terminology similar to 3GPPterminology is oftentimes used. However, the concepts disclosed herein are not limited to a 3GPP system.

[0104] Note that, in the description herein, reference may be made to the term "cell"; however, particularly with respect to 5G NR concepts, beams may be used instead of cells and, as such, it is important to note that the concepts described herein are equally applicable to both cells and beams.

[0105] There are certain challenges with existing technology. In a hybrid network including both Terrestrial Network (TN) and Non-Terrestrial Network (NTN) cells, the UE can be configured by a network node to perform measurements on both TN cells and NTN cells. In a low activity state (e.g. a low activity Radio Resource Control (RRC) state such as, e.g., RRC_IDLE or RRC_IN ACTIVE), according to the existing technology, a User Equipment (UE) served by a TN cell may perform a cell change (e.g. cell reselection) to one of the neighboring TN and NTN cells, whichever is better ranked i.e. which has better received signal level (e.g. higher Reference Signal Received Power (RSRP)), also taking carrier frequency priorities into account.

[0106] In RRC_CONNECTED state, according to the existing technology, a UE served by a TN cell may perform a cell change (e.g. handover, which is also referred to as reconfiguration with sync, or conditional handover) to one of the neighboring TN and NTN cells based on respective command (e.g., RRCReconfiguration command) from the gNodeB (gNB), where the gNB's handover decision or the execution condition of the conditional handover is typically based on the UE's measured received signal level (e.g. higher RSRP) in the source and target cells.

[0107] One issue is that a UE does not always enable and maintain Global Navigation Satellite System (GNSS) positioning while residing (connected or camping) in a TN cell because such position measurements consume energy and are not needed for operation in a TN. However, when the UE performs a cell change (e.g., cell reselection in low activity RRC state or handover in RRC connected state) to an NTN cell, the UE is required to acquire and maintain GNSS position measurement for the purpose of uplink (UL) synchronization (e.g., timing advance and / or Doppler pre-com pensation) and measurements on neighbor NTN cells.

[0108] The problematic consequence is that the cell change to the NTN cell may in practice be delayed for a significant amount of time while the UE performs a timeconsuming GNSS measurement. Note that a GNSS measurement can take anywherebetween half a second and multiple tens of seconds (or even minutes), depending on the UE's current GNSS state (e.g., cold, warm, or hot state). A UE in RRCJDLE or RRC_INACTIVE state can start to monitor the downlink signals in the new NTN cell, but the UE cannot access the NTN cell until it has obtained a valid position measurement from the GNSS measurement. A UE in RRC_CONNECTED state will have to delay the execution of the handover that the UE has been ordered to execute because, before the UE can access the target NTN cell, the UE has to perform a GNSS measurement to determine its own location so it can calculate the Timing Advance (TA) to use when transmitting (e.g., a random access preamble) in the target NTN cell. Considering the large amount of time that a GNSS measurement can be expected to take, this is likely to cause the handover supervision timer (i.e., timer T304 in NR) to expire, resulting in handover failure. The issue is worse when the GNSS receiver in the UE is in 'cold start' state. Another practical problem that a UE in a TN cell may encounter is that its GNSS positioning may be unavailable due to any reason (e.g., temporary inability to receive GNSS signals) even if the UE is running GNSS positioning operation.

[0109] Embodiments of systems and methods that address the aforementioned and / or other challenges are disclosed herein. Embodiments of the present disclosure addresses the above-described challenges by validating UE positioning in an NTN cell (e.g., the target NTN for a cell switch procedure from a serving (source) TN cell (to the target NTN cell) with respect to new position assistance information as substitute to a GNSS positioning measurement. The position assistance information is provided to the UE in the serving TN cell (Celli) by the serving network node (e.g., serving gNB in the case of NR), e.g., in the form of geographical coordinates per Synchronization Signal Block (SSB) beam (or some other more compact representation) in the serving TN cell (Celli). The position assistance information may be provided to the UE, e.g., by broadcast information (e.g., broadcasting a SIB) or dedicated signaling (e.g., RRC signaling or MAC CE signaling). The UE can find or select a position provided in the position assistance information, or derive a position from or based on the position assistance information, to use as the UE's own position when performing operations related to a neighboring NTN cell (Cell2) (e.g., the target NTN cell for a cell switch). For example, the UE may use the selected or derived position from the position assistance information to perform measurements on the NTN cell (Cel 12) for assessment of apotential cell reselection or to access the NTN cell (Cell2), e.g. in conjunction with a handover to the NTN cell (Cell2).

[0110] In the preferred embodiments, the UE is served by the TN cell (Celli), which in turn is served or managed or operated by a first TN node (NW1). The NTN cell (Cell2) is neighboring with the TN cell (Celli), which in turn is served or managed or operated by a second NTN node (NW2). The UE is capable of operating in both TN and NTN.

[0111] In case that GNSS positioning is required by ongoing or future operations in NTN cell (Cell2) but GNSS measurement by the UE served by TN Cell (Celli) would take too long or GNSS is temporarily unavailable, the position assistance information provided to the UE is used by the UE to estimate its position in the NTN cell (Cell2) while in low activity RRC state or RRC connected state.

[0112] In one embodiment, a UE capable of operating in both a TN and a NTN (and, e.g., capable of receiving and using position assistance information as described herein) is provided (by a network node such as, e.g., a network node operating a serving TN cell of the UE) with position assistance information that allows the UE to determine a sufficiently accurate estimate of the position of the UE for one or more operations in a NTN cell without GNSS measurement.

[0113] While not being limited to or by any particular advantage, embodiments of the present disclosure may provide a number of advantages over the existing technology. The position assistance information disclosed herein can enable a UE to validate and maintain a valid position before cell change to an NTN cell, which is a prerequisite to be able to setup UL synchronization (timing advance and / or Doppler precompensation) and perform measurements on neighbor NTN cells without any delay after being served by the NTN cell. This in turn improves efficiency of mobility between TN and NTN.

[0114] Now, the description will turn to a more detailed description of embodiments of the present disclosure. Embodiments of the proposed solution are described below mainly in terms of NR NTN, but the solution is equally applicable to loT NTN. Adapting the embodiments disclosed herein to loT NTN implies minor adjustments such as straightforward changes of terminology, e.g. that a base station should be considered to be an evolved NodeB (eNB) rather than a gNB, and that the inter-base station communication protocol is X2AP instead of XnAP.

[0115] The term "satellite" may also be referred to herein as a satellite node, satellite access node (SAN), an NTN node, node in space, etc. A base station (BS) or radio network node (RNN) associated with a satellite might include both a regenerative satellite, where the BS or RNN is the satellite payload, i.e. the BS or RNN is integrated with the satellite, or a transparent satellite, where the satellite payload is a relay and BS or RNN is on the ground (i.e., the satellite relays the communication between the BS or RNN on the ground and the UE).

[0116] The term "node" is used herein to refer to either a network node or a User Equipment (UE). Examples of network nodes are NodeB, base station (BS), MultiStandard Radio (MSR) radio node such as MSR BS, eNB, gNB, Master eNB (MeNB), Secondary eNB (SeNB), Satellite Access Node (SAN), Location Measurement Unit (LMU), Integrated Access Backhaul (IAB) node, network controller, Radio Network Controller (RNC), Base Station Controller (BSC), relay, donor node controlling relay, Base Transceiver Station (BTS), Central Unit (e.g. in a gNB), Distributed Unit (e.g. in a gNB), Baseband Unit, Centralized Baseband, Cloud Radio Access Network (C-RAN), Access Point (AP), transmission points, transmission nodes, Transmission Reception Point (TRP), Remote Radio Unit (RRU), Remote Radio Head (RRH), nodes in Distributed Antenna System (DAS), core network node (e.g. Access and Mobility management Function (AMF) in the case of 5GC, Mobility Management Entity (MME) in the case of EPC, etc.), Operations and Maintenance (O&M), Operations Support System (OSS), SelfOrganizing Network (SON) node, positioning node (e.g. Evolved Serving Mobile Location Center (E-SMLC)), etc.

[0117] The non-limiting term "UE" refers to any type of wireless device communicating with a network node and / or with another UE in a cellular or mobile communication system. Examples of UE are target device, Device to Device (D2D) UE, Vehicular to Vehicular (V2V), machine type UE, Machine Type Communication (MTC) UE or UE capable of Machine to Machine (M2M) communication, Personal Digital Assistant (PDA), tablet, mobile terminals, smart phone, Laptop Embedded Equipment (LEE), Laptop Mounted Equipment (LME), Universal Serial Bus (USB) dongles, etc.

[0118] The term "radio access technology", or RAT, may refer to any RAT, e.g. Universal Terrestrial Radio Access (UTRA), Evolved UTRA (E-UTRA), Narrow Band Internet of Things (NB-IoT), WiFi, Bluetooth, next generation RAT, New Radio (NR), 4G, 5G, 6G, NR NTN, loT NTN, LTE NTN, etc. Any of the equipment denoted by the termnode, network node, or radio network node may be capable of supporting a single or multiple RATs.

[0119] The term "signal" or "radio signal" as used herein can be any physical signal or physical channel. Examples of downlink (DL) physical signals are Reference Signals (RSs) such as Cell-specific RS (CRS), NR-IoT RS (NRS), Narrowband Primary Synchronization Signal (NPSS), Narrowband Secondary Synchronization Signal (NSSS), Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS), Channel State Information RS (CSI-RS), Demodulation Reference Signal (DMRS) signals in Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) Block (SSB), Discovery Reference Signal (DRS), Positioning Reference Signal (PRS), etc. RS may be periodic, e.g. RS occasion carrying one or more RSs may occur with certain periodicity, e.g. 20 milliseconds (ms), 40 ms, etc. The RS may also be aperiodic. Each SSB carries NR-PSS, NR-SSS and NR-PBCH in 4 successive symbols. One or multiple SSBs are transmitted in one SSB burst which is repeated with certain periodicity, e.g. 5 ms, 10 ms, 20 ms, 40 ms, 80 ms, or 160 ms. The UE is configured with information about SSBs on cells of a certain carrier frequency by one or more SSB Measurement Timing Configuration (SMTC) configurations. The SMTC configuration comprises parameters such as SMTC periodicity, SMTC occasion length in time or duration, SMTC time offset with regards to a reference time (e.g. serving cell's System Frame Number (SFN)), etc. Therefore, an SMTC occasion may also occur with certain periodicity, e.g. 5 ms, 10 ms, 20 ms, 40 ms, 80 ms, or 160 ms. Examples of uplink (UL) physical signals are RSs such as Sounding Reference Signal (SRS), DMRS, etc. The term "physical channel" refers to any channel carrying higher layer information, e.g. data, control, etc. Examples of physical channels are PBCH, Narrowband PBCH (NPBCH), Physical Downlink Control Channel (PDCCH), Physical Downlink Shared Channel (PDSCH), Physical Uplink Control Channel (PUCCH), Physical Uplink Shared Channel (PUSCH), short PDSCH (sPDSCH), short PUCCH (sPUCCH), short PUSCH (sPUSCH), MTC PDCCH (MPDCCH), Narrowband PDCCH (NPDCCH), Narrowband PDSCH (NPDSCH), Enhanced PDCCH (E-PDCCH), Narrowband PUSCH (NPUSCH), etc.

[0120] The term "carrier frequency" used herein is also referred to as Component Carrier (CC), frequency layer, layer, carrier, frequency, serving carrier, frequency channel, radio channel, radio frequency channel, Positioning Frequency Layer (PFL), Measurement Object (MO), etc. The carrier frequency belongs to a certain frequencyband, which may contain one or multiple carrier frequencies based on its passband (e.g., size of the band in frequency domain) and / or bandwidth of the carriers and / or the channel raster etc. The carrier frequency related information is transmitted to the UE by a network node using a frequency channel number identifier via a message, e.g. Radio Resource Control (RRC) message. Examples of the channel number or identifier, which may be pre-defined, are Absolute Radio Frequency Channel Number (ARFCN), NR- ARFCN, etc.

[0121] The term "time resource" as used herein may correspond to any type of physical resource or radio resource expressed in terms of length of time. Examples of time resources are: symbol, time slot, subframe, radio frame, Transmission Time Interval (TTI), interleaving time, slot, sub-slot, mini-slot, System Frame Number (SFN) cycle, Hyper-SFN (H-SFN) cycle, etc.

[0122] The term Non-Terrestrial Network (NTN) as used herein may, depending on the context, refer to either or both of NR NTN and loT NTN, and sometimes the term is used to refer to only NR NTN. Thus, even though the embodiments outlined below are described mainly in terms of NR based NTNs, they are equally applicable in an NTN based on LTE technology and in particular loT NTN and similar future NTNs (e.g., an NTN in a 6thGeneration (6G) system).

[0123] The terms "serving TN cell" and "TN serving cell" are used herein interchangeably.

[0124] Any expression used herein stating that a cell performs an action (e.g., that the serving TN cell sends a message to the UE) should be interpreted as a simplified way of writing that the base station (BS) serving the cell performs an action (e.g., that the BS serving the serving TN cell sends a message to the UE).

[0125] The terms "serving node", "source node", "serving / source node", "source / serving node", "target node", "candidate target node", "serving BS", "source BS", "serving / source BS", "source / serving BS", "target BS" and "candidate target BS" may sometimes be used herein. The "node" or "BS" in these terms should be understood as typically being a Radio Access Network (RAN) node (e.g., an RNN) in an NTN based on NR technology, LTE technology, or any other RAT in which handover, conditional handover, or another mobility or conditional mobility concept is defined. In an NR based NTN, such a RAN node may be assumed to be a gNB. In an LTE based NTN (including an loT NTN), such a RAN node may be assumed to be an eNB.Alternatives to, or refinements of, these interpretations are however also conceivable. For instance, a gNB may be an en-gNB, and if a split gNB architecture is applied (dividing the gNB into multiple separate entities or notes), the term "node" may refer to a part of the gNB, such as a gNB-CU (often referred to as just CU), a gNB-DU (often referred to as just DU), a gNB-CU-Control Plane (CP) or a gNB-CU-User Plane (UP). Similarly, an eNB may be an ng-eNB, and if a split eNB architecture is applied (dividing the eNB into multiple separate entities or notes), the term "node" may refer to a part of the eNB, such as an eNB-CU, an eNB-DU, an eNB-CU-CP or an eNB-CU-UP. Furthermore, the "node" in the terms may also refer to an lAB-donor, lAB-donor-CU, lAB-donor-DU, lAB-donor-CU-CP, or an lAB-donor-CU-UP.

[0126] The various embodiments described herein are often described in conjunction with handover (reconfiguration with sync) or conditional handover (CHO). However, these embodiments are also applicable in conjunction with other mobility procedures and conditional mobility procedures in RRC_CONNECTED state. For instance, Primary Secondary Cell (PSCell) change, PSCell addition, Secondary Cell (SCell) addition, conditional PSCell change, and conditional PSCell addition.

[0127] When writing message names of a communication protocol, two equivalent principles are used herein. The writing principle "<protocol name> <message name> message", for example "XnAP HANDOVER REQUEST message", and the writing principle "<message name> <protocol name> message", for example "HANDOVER REQUEST XnAP message" are equivalent, both referring to a message (i.e., "<message name>") of a communication protocol (i.e., "<protocol name>"), e.g. the HANDOVER REQUEST message of the communication protocol XnAP. The same writing format equivalence applies to other communication protocols, such as Next Generation Application Protocol (NGAP).

[0128] The terms "Handover Command", "Handovercommand", and "HO Command" are used interchangeably herein. Those terms all refer to a UE configuration the target node (of a regular handover) or candidate target node (of a conditional handover), during the (conditional) handover preparation phase, compiles for the UE to be subject to the handover or conditional handover. This UE configuration is compiled in the form of an RRCReconfiguration message which is conveyed to the UE via the source node. The RRCReconfiguration is associated with a certain target cell or candidate target celland the UE applies the RRCReconfigu ration when / if it accesses the concerned (candidate) target cell controlled by the (candidate) target node.

[0129] When Conditional Handover (CHO) is configured for a UE, a cell which the UE potentially can connect to (i.e., if the CHO execution condition is fulfilled for the cell) is denoted as "candidate target cell". Similarly, a RAN node controlling a candidate target cell is denoted as "candidate target node". However, once the UE has detected a fulfilled CHO execution condition for a candidate target cell, this terminology becomes a bit blurred. At this point, during the actual execution of the CHO and when the UE has connected to the new cell, the concerned cell may be referred to as either a "candidate target cell" or a "target cell". Similarly, a RAN node controlling such a cell, may in this situation be referred to as either a "candidate target node" or a "target node". Despite this discussion of the proper terminology for CHO, in this solution description, the word "candidate" is often skipped for simplicity (partly because the typical scenario is that there is only one candidate target cell). That is, the terms "target node", "target gNB" and "target cell" may be used even when it would be more proper to use the terms "candidate target node", "candidate target gNB" and "candidate target cell".

[0130] A condition included in a CHO configuration governing the execution of the conditionally configured procedure may be referred to as either a "CHO execution condition" or a "HO execution condition". Similarly, phases of the procedure may be referred to as the Handover Preparation phase, the Handover Execution and / or the Handover Completion phase, or may be referred to as the Conditional Handover Preparation phase, the Conditional Handover Execution phase and / or the Conditional Handover Completion phase.

[0131] Figure 6 illustrates one example of a system 600 in which embodiments of the present disclosure may be implemented. As illustrated, the system 600 includes a UE 602 served by a Terrestrial Network (TN) cell 604, which is served or managed or operated by a TN node 606 (e.g., a RNN or BS such as, e.g., a gNB or an eNB, belonging to the TN). The TN cell 604 operates on a first TN carrier frequency (Fll). The UE 602 is located in the TN cell 604, e.g., in RRC_CONNECTED, RRCJNACTIVE, or RRC_IDLE state, and the UE 602 is configured to perform measurements on at least one carrier frequency (F21) operated by or belonging to an NTN. F21 can be intrafrequency, inter-frequency, or inter-RAT carrier frequency in relation to the TN cell 604 operating on Fll. In this example, F21 is operated by an NTN node 608. An example ofthe NTN node 608 is a satellite node, which, as described above, may also be referred to herein as a SAN. As an example, the NTN node 608 manages or serves or operates or controls one or more NTN cells 610 belonging to F21. The NTN node 608 may host a BS, e.g., a gNB or an eNB, or it may serve as a relay between UEs and a BS (via a GW) on the ground.

[0132] In case that GNSS measurement by the UE 602 served by the TN cell 604 would take too long or GNSS is temporarily unavailable, it brings difficulties for the UE 602 to measure the neighbor NTN cell(s) 610 before cell change to one of the neighboring NTN cell(s) 610 and / or to determine a TA for random access preamble transmission on the neighboring NTN cell(s) 610. In this case, a solution is proposed herein to enable the TN node 606 operating the TN cell 604 to provide position assistance information to the UE 602 that the UE 602 can use to determine a position of the UE 602, e.g., as a substitute for GNSS positioning.

[0133] Figure 7 is a flow chart that illustrates the operation of the UE 602 and the TN node 606 in accordance with embodiments of the present disclosure. As illustrated, the TN node 606 provides position assistance information to the UE 602 (step 702). The position assistance information is information that allows the UE 602 to choose or determine an estimate of the position of the UE 602, e.g., while the UE 602 is in a low activity RRC state (e.g., RRCJDLE or RRC_INACTIVE state) or RRC_CONNECTED state. In one example, the TN node 606 provides the position assistance information to UEs (including the UE 602) on the TN cell 604 via broadcasted system information. Optionally, this broadcasted position assistance information targets UEs in RRC_INACTIVE and RRCJDLE states. In one embodiment, the position assistance information is included in a System Information Block (SIB) or possibly in multiple SIBs, e.g., divided into parts where different parts are included in different SIBs. Optionally, using broadcast information to convey the position assistance information would (primarily) be intended for UEs in low activity RRC state (i.e., UEs in RRCJNACTIVE state and RRCJDLE state), but as another option, UEs in RRC_CONNETED state can also receive the position system information via the broadcast information. In one example, the SIB can be configured to be on-demand to avoid the signaling load of numerous (potentially redundant) transmissions of the position assistance information. This may for instance be a new SIB, e.g., introduced for this purpose. In another example, the TN node 606 provides the position assistance information to the UE 602on the TN cell 604 via a dedicated message while the UE 602 is in RRC_CONNEDCTED state, e.g. an RRC message, a Medium Access Control (MAC)-Control Element (CE), or a Downlink Control Information (DCI) message.

[0134] In one example alternative embodiment not illustrated in Figure 7, the UE 602 obtains the position assistance information using a network-based (or network-involved) UE positioning procedure, e.g. a positioning method in the LCS framework. To this end, the UE 602 may trigger, or the network may trigger, the UE 602 to acquire position information by a RAT-dependent positioning procedure in the serving TN cell 604, e.g. a positioning procedure in the LCS framework, wherein the resulting UE position information may be regarded as the position assistance information to be used by the UE 602 for neighbor NTN cell measurements or UL synchronization in a neighbor NTN cell (e.g. as part of a cell change such as a handover / reconfiguration with sync to a neighbor NTN cell).

[0135] From the UE's perspective, if the UE 602 is aware of its need to know its own position (to some level of accuracy) for procedures related to one or more neighbor NTN cell(s) 610, e.g. neighbor cell measurements and / or TA calculation, e.g. due to a potential cell change to an NTN cell 610 (e.g. cell reselection if the UE 602 is in a low activity RRC state or handover if the UE 602 is in RRC_CONNECTED state), and the UE 602 currently does not have valid UE position information and currently cannot perform a GNSS measurement, or cannot perform a GNSS measurement within a required time, the UE 602 obtains the position assistance information (step 704). This may include receiving position assistance information from the TN node 606 on the TN cell 604 via broadcast information (e.g., via a broadcast SIB). In some cases, the broadcast information containing the position assistance information (e.g., SIB(s) including the position assistance information) are transmitted by the TN node 606 on-demand, and this may require that the UE 602 first sends, to the TN node 606, a request for broadcast of a SI message(s) (e.g., a SIB(s)) containing the position assistance information (step 700).

[0136] Alternatively, if the UE 602 is in RRC_CONNECTED state, the obtaining (or attempt to obtain) the position assistance information may include receiving a dedicated (i.e., not broadcast but addressed to the UE) message (e.g., an RRC message, a MAC CE or a DCI message) including the position assistance information. The TN node 606 may be triggered to send the dedicated message by a preceding request from the UE602 to receive the position assistance information or an indication from the UE 602 that it lacks valid UE position information (step 700). The indication also may indicate that the UE 602 will not be able to autonomously obtain valid UE position information (e.g., through a GNSS measurement) fast enough e.g., for successful execution of a procedure that triggered the need for the UE position information, or that the UE 602 lacks support for GNSS position measurements. As yet another alternative for the case where the UE 602 is in RRC_CONNECTED state, the obtaining (or attempt to obtain) the position assistance information may involve triggering, or requesting the network to initiate, a network-based (or network-involved) UE positioning measurement, e.g., using a procedure in the LCS framework.

[0137] In one embodiment, the position assistance information may include position assistance information for the TN cell 604 and one or more additional (e.g., neighboring) TN cells. In that case, for each TN cell for which position assistance information is provided, the broadcast information or dedicated message(s) containing the position assistance information may further comprise TN cell information that indicates the TN cell to which the position assistance information applies. The TN cell information may include, for example, one or more of a Physical Cell Identity (PCI) of the TN cell, a NR Cell Global Identity (NCGI) of the TN cell, a carrier frequency of the TN cell, an ARFCN of the TN cell, a Public Land Mobile Network (PLMN) identity of a PLMN to which the TN cell belongs, a Tracking Area Identity (TAI) of a tracking area in which the TN cell is included, a Tracking Area Code (TAC) of the tracking area in which the TN cell is included, etc.. Position assistance information associated with one or more neighboring TN cells may be provided in addition to the position assistance information associated with the serving TN cell 604. In the case of broadcasting the position assistance information, the position assistance information for the one or more neighboring TN cells may be included in the same broadcast information (e.g., in the same SIB) as the position assistance information associated with the serving TN cell 604 or may be included in one or more other SIBs (e.g., SIB3 which contains intrafrequency neighbor cell information and / or SIB4 which contains inter-frequency neighbor cell information.

[0138] The motivation for the option to provide position assistance information for one or more neighboring TN cells is that it may complement the position assistance information associated with the serving TN cell 604, which may be useful in particularfor a fast-moving UE. Compared with NTN cell coverage, TN cell coverage normally has rather smaller size. A UE capable of operation in both a TN and an NTN may cross more than one TN cell while still staying in the coverage of the same NTN cell. In this case, position assistance information for more than one TN cell may be beneficial when selecting or deriving an estimate of the position of the UE 602.

[0139] The UE 602 then obtains a position of the UE 602 (i.e., estimates the position of the UE 602) based on the obtained position assistance information for the TN cell 604 and, optionally, position assistance for one or more additional (e.g., neighboring) TN cells (step 706). In one example, an approximate position of the UE 602 can be acquired based on the position assistance information obtained for the TN cell 604. In another example, an approximate position of the UE 602 can be acquired based on the position assistance information provided by a previously serving TN cell of the UE 602. In another example, the position of the UE 602 can be estimated based on combining position assistance information provided by one or more previously serving TN cells and the current serving TN cell 604 of the UE 602. In another example, the position of the UE 602 can be estimated based on a combining position assistance information associated with the serving TN cell 604 and position assistance information associated with one or more neighboring TN cells. In yet another example, the position of the UE 602 can be estimated based on combining position assistance information associated with one or more neighboring TN cells. In the above examples, combining the position assistance information associated with different cells may involve calculating an average position, a weighted average position (e.g. giving different weights to different ones of the position estimates obtained from the position assistance information associated with different cells), or any other calculation to obtain a UE position estimate based on the position estimates obtained from the position assistance information associated with the different cells.

[0140] A particular example is that the position assistance information obtained from the TN node 606 includes an antenna site location (e.g., geographical coordinates of the location of the antenna site) of the antenna which the TN node 606 uses for downlink transmissions and uplink receptions in the serving TN cell 604 of the UE 602. In this case, the UE 602 may use geographical coordinates of the antenna site location as the position (i.e., estimate of the position) of the UE 602. As discussed below, this position estimate may be used by the UE 602 (in step 708) for neighbor NTN cell measurementsand / or uplink synchronization in a neighbor NTN cell 610 (e.g., as part of a cell change such as a handover / reconfiguration with sync to a neighbor NTN cell).

[0141] As another example, in order to achieve the highest possible accuracy without positioning measurements performed by the UE 602 and without potentially timeconsuming and potentially unavailable network-based (or network-involved) UE positioning measurements, the position assistance information includes information that enables the UE 602 to choose a position to use as its own position, and preferably includes at the least information that provides a mapping between geographical coordinates in the serving TN cell 604 and information the UE 602 can acquire from the serving TN cell 604, e.g. indexes of SSB beams. In other words, the UE 602 can determine the geographical coordinates to use as its position with respect to the SSB beam (e.g., an SSB beam having a highest RSRP or similar measurement) detected at the UE 602. As one particular example, the position assistance information includes an antenna site location (e.g., in terms of geographical coordinates) which is a common source for all SSB beams (i.e., it is a common reference location for the SSB beams) and a beam direction for each SSB beam. Then, the UE can estimate its location based on the antenna site location, the beam direction of the SSB beam in which the UE 602 is located, and the UE's current TA, where the TA is approximately equal to the RTT between the UE 602 and the antenna site and which thus enables calculation of theUE's distance D from the antenna site as D = where c is the speed of light in vacuum, n is the refraction index in air, and TA is the UE's timing advance. The position assistance information in this example may be refined, in another example, to also include the RTT (here denoted as RTTfronthaui) or propagation time (i.e. RTT / 2, here denoted as Pfronthaui) of the fronthaul, or more precisely, between the antenna and the UL / DL alignment point, i.e. the uplink time synchronization reference point, i.e. the reference point for the UE's TA, which typically is an antenna port, or an interface at the gNB (e.g. the DU). With this refined position assistance information, the UE's distance D from the antenna site can be calculated as D =C X(TA RTTfronthaulThe UE 602 typically acquires position assistance information from its serving TN cell 604, but as an option, the UE 602 may also acquire position assistance information from one or more other TN cell(s), e.g. one or more neighbor TN cell(s).

[0142] As another example, to reduce the amount of data in the position assistance information while still providing SSB beam granularity, the position assistance information is, in one example, signaled as follows (when the SSB configuration is such that it works):• For a cell served by an omnidirectional (at least in the horizontal plane) gNB antenna: The position assistance information includes the location of the antenna site (and optionally also RTTfronthaui or Pfronthaui) and the direction of one SSB beam, e.g. SSB 0 (i.e., SSB with index 0). The UE 602 knows the number of SSB beams from the system information and can then assume that the SSB beams are distributed with equal angles in between around the full circle. By combining the gNB antenna site location (and RTTfronthaui or Pfronthaui, if this is included in the position assistance information) with the direction of the UE's current SSB beam and the UE's current TA (which gives the distance from the gNB antenna site location to the UE in the direction indicated by the SSB beam direction), the UE is able to determine a sufficiently accurate position to use as its own position, e.g. when calculating the TA to use for a random access preamble transmission in a neighbor NTN cell (e.g. in conjunction with a handover where the neighbor NTN cell is the target cell).• For a cell served by a gNB sector antenna: The position assistance information includes the location of the antenna site (and optionally also RTTfronthaui or Pfronthaui) and the direction of the two edge SSB beams. The UE knows the number of SSBs from the system information and can then assume that the SSB beams are distributed with equal angles in between within the sector defined by the two indicated edge beam directions. By combining the gNB antenna site location (and RTTfronthaui or Pfronthaui, if this is included in the position assistance information) with the direction of the UE's current SSB beam and the UE's current TA (which gives the distance from the gNB antenna site location to the UE in the direction indicated by the SSB beam direction), the UE is able to determine a sufficiently accurate position to use as its own position, e.g. when calculating the TA to use for a random access preamble transmission in a neighbor NTN cell (e.g. in conjunction with a handover where the neighbor NTN cell is the target cell).

[0143] An example of one embodiment of the position assistance information defined in ASN.l (realizing the above examples of compact position assistance information associated with a cell served by a gNB sector antenna or a gNB omnidirectional (at least in the horizontal plane) antenna) is provided below. The example ASN.l code shows the definition of an Information Element (IE) tentatively denoted as " PositionAssistancelnfo- rXX'. This IE is, in one embodiment, included in a SIB, which could be an existing SIB, e.g., SIB19, or a new SIB. Table 2 illustrates field descriptions describing the fields / parameters in the example ASN.l code below.PositionAssistancelnfo-rXX : : = SEQUENCE { antennaLocation-rXX OCTET STRING, startSSB-Direction-rXX SSB-Direction-rXX OPTIONAL, endSSB-Direction-rXX SSB-Direction-rXX OPTIONAL}SSB-Direction-rXX : : = SEQUENCE { ssb-Index-rXX SSB-Index, direction-rXX INTEGER (0..359) }Table 2: Field Descriptions

[0144] Note that the parameter type SSB-Index\s already defined in the existing RRC specification, i.e. 3GPP TS 38.331 version 17.5.0, where it is defined as follows:SSB-Index : := INTEGER (0..maxNrofSSBs-l)

[0145] In another example, the position assistance information includes a position (which is independent of the UE's TA and thus independent of the UE's actual position or distance from the antenna) for each SSB. These positions could be provided in the form of geographical coordinates, e.g., using the Ellipsoid-Point parameter type, as defined in 3GPP TS 37.355 version 17.5.0. But more compact ways of representing these positions are conceivable, similar to the above-described compact representations of SSB beam directions. To provide a position per SSB, these above-described compact SSB beam direction representations could be complemented with a distance from the antenna location - to be applied in the direction of each SSB beam - to the position of each respective SSB (i.e., all SSB positions are located at the same distance, but in different directions, from the antenna location. The full position assistance information for a position per SSB would thus be:• For a cell served by an omnidirectional (at least in the horizontal plane) gNB antenna: The position assistance information includes the location of the antenna site, the distance (Dpos) from the antenna site location to a position (to be applied in each SSB beam's direction, i.e. the same distance is valid for all SSBs' associated positions), and the direction of one SSB beam, e.g. SSB 0 (i.e., SSB with index 0). The UE knows the number of SSBs from the system information and can then assume that the SSB beams are distributed with equal angles in between around the full circle. A UE can calculate the position associated with a certain SSB as the position located a distance Dposfrom the antenna site location in the direction of the concerned SSB beam (assumedly the SSB beam the UE is using). Unless the cell is too large, this position should be sufficiently accurate for the UE to use as its own position, e.g., when calculating the TA to use for a random access preamble transmission in a neighbor NTN cell (e.g., in conjunction with a handover where the neighbor NTN cell is the target cell).• For a cell served by a gNB sector antenna: The position assistance information includes the location of the antenna site, the distance (Dpos) from the antennasite location to a position (to be applied in each SSB beam's direction, i.e. the same distance is valid for all SSBs' associated positions), and the direction of the two edge SSB beams. The UE knows the number of SSBs from the system information and can then assume that the SSB beams are distributed with equal angles in between within the sector defined by the two indicated edge beam directions. A UE can calculate the position associated with a certain SSB as the position located a distance Dposfrom the antenna site location in the direction of the concerned SSB beam (assumedly the SSB beam the UE is using). Unless the cell is too large, this position should be sufficiently accurate for the UE to use as its own position, e.g., when calculating the TA to use for a random access preamble transmission in a neighbor NTN cell (e.g., in conjunction with a handover where the neighbor NTN cell is the target cell).

[0146] In other example of compact representation of positions per SSB, the position assistance information includes position information, e.g. geographical coordinates (e.g. in the form of the Ellipsoid-Point parameter type, as defined in 3GPP TS 37.355 version 17.5.0), for the antenna site location, and for one SSB beam (if the cell is served by an omnidirectional (at least in the horizontal plane) gNB antenna) or for two sector edge SSB beams (if the cell is served by a sector gNB antenna). As before, the UE knows the number of SSBs (or more precisely SSB beams) in the cell from the system information and will assume that the SSB beams are distributed with equal angles in between around the full circle (in case of an omnidirectional (at least in the horizontal plane) gNB antenna) or within the sector defined by the two sector edge SSB beams (in case of a Sector gNB antenna). The UE further assumes that the positions associated with all SSBs are located an equally long distance from the antenna site location, albeit in different directions. The full position assistance information for a position per SSB would thus be:• For a cell served by an omnidirectional (at least in the horizontal plane) gNB antenna: The position assistance information includes the location of the antenna site and the position associated with one SSB beam, e.g. SSB 0 (i.e., SSB with index 0). The UE knows the number of SSBs from the system information and can then assume that the SSB beams are distributed with equal angles in between around the full circle, and that the positions associated with all SSBs are located at the same distance from the antenna site location. The UE can calculatethis distance as the distance between the one SSB-associated position provided in the position assistance information and the antenna site location. This means that the UE can assume that the positions of the SSBs are equidistantly located on a circle with its center at the antenna site location and a radius equal to the distance between the antenna site location and any of the positions associated with an SSB. Unless the cell is too large, the position associated with the UE's current SSB should be sufficiently accurate for the UE to use as its own position, e.g. when calculating the TA to use for a random access preamble transmission in a neighbor NTN cell (e.g., in conjunction with a handover where the neighbor NTN cell is the target cell).• For a cell served by a gNB sector antenna: The position assistance information includes the location of the antenna site and the positions associated with the two sector edge SSB beams, e.g. SSB 0 (i.e., SSB with index 0). The UE knows the number of SSBs from the system information and can then assume that the SSB beams are distributed with equal angles in between within the circle sector defined by the two sector edge SSB beams, and that the positions associated with all SSBs are located at the same distance from the antenna site location. The UE can calculate this distance as the distance between one of the SSB- associated positions provided in the position assistance information and the antenna site location. This means that the UE can assume that the positions of the SSBs are equidistantly located on a circle sector with its center at the antenna site location and a radius equal to the distance between the antenna site location and any of the positions associated with an SSB. Unless the cell is too large, the position associated with the UE's current SSB should be sufficiently accurate for the UE to use as its own position, e.g. when calculating the TA to use for a random access preamble transmission in a neighbor NTN cell (e.g., in conjunction with a handover where the neighbor NTN cell is the target cell).

[0147] The UE 602 uses the position of the UE 602 obtained based on the position assistance information in step 706 to perform one or more actions relative to one or more neighboring NTN cells (step 708). For example, the UE 602 may use the position obtained in step 706 to perform measurements on one or more neighboring NTN cells 610 and / or to perform uplink synchronization (e.g., TA and / or Doppler shift) to aparticular NTN cell 610 (e.g., in order to transmit a random access preamble on the NTN cell 610).

[0148] With some adaptation, the above-described solutions / embodiments / example can also be applicable to a UE served by an NTN cell in a location which is also covered by a TN cell. In this situation, if the UE served by the NTN cell requires obtaining (e.g. updating) its own position information, but cannot perform a GNSS measurement due to some reasons (e.g. that the UE cannot receive signals from sufficiently many GNSS satellites), then the UE is able to read the position assistance information broadcasted in the (neighbor) TN cell covering the UE, and derive an estimate of its own position from the broadcasted position assistance information. The UE can then use the determined estimate of its own position in any operation in the NTN requiring the UE position, such as UE autonomous adaptation of SMTC or UE autonomous calculation of the TA or determination of UE antenna direction or UE RX and / or TX beam direction.

[0149] Figure 8 is a schematic block diagram of a network node 800 according to some embodiments of the present disclosure. Optional features are represented by dashed boxes. The network node 800 may be, for example, the TN node 606 of Figure 6 or a network node that performs part of the functionality of the TN node 606 (e.g., a gNB-DU, a gNB-CU, a gNB-CU-CP, a gNB-CU-UP, an eNB-DU, an eNB-CU, an eNB-CU- CUP, an eNB-CU-UP, or the like). As illustrated, the network node 800 includes a control system 802 that includes one or more processors 804 (e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and / or the like), memory 806, and a network interface 808. The one or more processors 804 are also referred to herein as processing circuitry. In addition, the network node 800 may include one or more radio units 810 that each includes one or more transmitters 812 and one or more receivers 814 coupled to one or more antennas 816. The radio units 810 may be referred to or be part of radio interface circuitry. In some embodiments, the radio unit(s) 810 is external to the control system 802 and connected to the control system 802 via, e.g., a wired connection (e.g., an optical cable). However, in some other embodiments, the radio unit(s) 810 and potentially the antenna(s) 816 are integrated together with the control system 802. The one or more processors 804 operate to provide one or more functions of the network node 800 as described herein (e.g., one or more functions of the TN node 606 as described herein).In some embodiments, the function(s) are implemented in software that is stored, e.g., in the memory 806 and executed by the one or more processors 804.

[0150] Figure 9 is a schematic block diagram that illustrates a virtualized embodiment of the network node 800 according to some embodiments of the present disclosure. Again, optional features are represented by dashed boxes. As used herein, a "virtualized" network node is an implementation of the network node 800 in which at least a portion of the functionality of the network node 800 is implemented as a virtual component(s) (e.g., via a virtual machine(s) executing on a physical processing node(s) in a network(s)). As illustrated, in this example, the network node 800 may include the control system 802 and / or the one or more radio units 810, as described above. The control system 802 may be connected to the radio unit(s) 810 via, for example, an optical cable or the like. The radio access node 800 includes one or more processing nodes 900 coupled to or included as part of a network(s) 902. If present, the control system 802 or the radio unit(s) are connected to the processing node(s) 900 via the network 902. Each processing node 900 includes one or more processors 904 (e.g., CPUs, ASICs, FPGAs, and / or the like), memory 906, and a network interface 908.

[0151] In this example, functions 910 of the network node 800 described herein are implemented at the one or more processing nodes 900 or distributed across the one or more processing nodes 900 and the control system 802 and / or the radio unit(s) 810 in any desired manner. In some particular embodiments, some or all of the functions 910 of the network node 800 described herein are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) 900. As will be appreciated by one of ordinary skill in the art, additional signaling or communication between the processing node(s) 900 and the control system 802 is used in order to carry out at least some of the desired functions 910. Notably, in some embodiments, the control system 802 may not be included, in which case the radio unit(s) 810 communicates directly with the processing node(s) 900 via an appropriate network interface(s).

[0152] In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the network node 800 or a node (e.g., a processing node 900) implementing one or more of the functions 910 of the network node 800 in a virtual environment according to any of the embodiments described herein is provided. Insome embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory).

[0153] Figure 10 is a schematic block diagram of a UE 1000 (e.g., the UE 602) according to some embodiments of the present disclosure. As illustrated, the UE 1000 includes one or more processors 1002 (e.g., CPUs, ASICs, FPGAs, and / or the like), memory 1004, and one or more transceivers 1006 each including one or more transmitters 1008 and one or more receivers 1010 coupled to one or more antennas 1012. The transceiver(s) 1006 includes radio-front end circuitry connected to the antenna(s) 1012 that is configured to condition signals communicated between the antenna(s) 1012 and the processor(s) 1002, as will be appreciated by on of ordinary skill in the art. The processors 1002 are also referred to herein as processing circuitry. The transceivers 1006 are also referred to herein as radio circuitry. In some embodiments, the functionality of the UE 1000 (e.g., the functionality of the UE 602 described herein) may be fully or partially implemented in software that is, e.g., stored in the memory 1004 and executed by the processor(s) 1002. Note that the UE 1000 may include additional components not illustrated in Figure 10 such as, e.g., one or more user interface components (e.g., an input / output interface including a display, buttons, a touch screen, a microphone, a speaker(s), and / or the like and / or any other components for allowing input of information into the UE 1000 and / or allowing output of information from the UE 1000), a power supply (e.g., a battery and associated power circuitry), etc.

[0154] In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the UE 1000 according to any of the embodiments described herein is provided. In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory).

[0155] With reference to Figure 11, in accordance with an embodiment, a communication system includes a telecommunication network 1100, such as a 3GPP- type cellular network, which comprises an access network 1102, such as a RAN, and acore network 1104. The access network 1102 comprises a plurality of base stations 1106A, 1106B, 1106C, such as Node Bs, eNBs, gNBs, or other types of wireless Access Points (APs), each defining a corresponding coverage area 1108A, 1108B, 1108C. Each base station 1106A, 1106B, 1106C is connectable to the core network 1104 over a wired or wireless connection 1110. A first UE 1112 located in coverage area 1108C is configured to wirelessly connect to, or be paged by, the corresponding base station 1106C. A second UE 1114 in coverage area 1108A is wirelessly connectable to the corresponding base station 1106A. While a plurality of UEs 1112, 1114 are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station 1106.

[0156] The telecommunication network 1100 is itself connected to a host computer 1116, which may be embodied in the hardware and / or software of a standalone server, a cloud-implemented server, a distributed server, or as processing resources in a server farm. The host computer 1116 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. Connections 1118 and 1120 between the telecommunication network 1100 and the host computer 1116 may extend directly from the core network 1104 to the host computer 1116 or may go via an optional intermediate network 1122. The intermediate network 1122 may be one of, or a combination of more than one of, a public, private, or hosted network; the intermediate network 1122, if any, may be a backbone network or the Internet; in particular, the intermediate network 1122 may comprise two or more sub-networks (not shown).

[0157] The communication system of Figure 11 as a whole enables connectivity between the connected UEs 1112, 1114 and the host computer 1116. The connectivity may be described as an Over-the-Top (OTT) connection 1124. The host computer 1116 and the connected UEs 1112, 1114 are configured to communicate data and / or signaling via the OTT connection 1124, using the access network 1102, the core network 1104, any intermediate network 1122, and possible further infrastructure (not shown) as intermediaries. The OTT connection 1124 may be transparent in the sense that the participating communication devices through which the OTT connection 1124 passes are unaware of routing of uplink and downlink communications. For example, the base station 1106 may not or need not be informed about the past routing of anincoming downlink communication with data originating from the host computer 1116 to be forwarded (e.g., handed over) to a connected UE 1112. Similarly, the base station 1106 need not be aware of the future routing of an outgoing uplink communication originating from the UE 1112 towards the host computer 1116.

[0158] Example implementations, in accordance with an embodiment, of the UE, base station, and host computer discussed in the preceding paragraphs will now be described with reference to Figure 12. In a communication system 1200, a host computer 1202 comprises hardware 1204 including a communication interface 1206 configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system 1200. The host computer 1202 further comprises processing circuitry 1208, which may have storage and / or processing capabilities. In particular, the processing circuitry 1208 may comprise one or more programmable processors, ASICs, FPGAs, or combinations of these (not shown) adapted to execute instructions. The host computer 1202 further comprises software 1210, which is stored in or accessible by the host computer 1202 and executable by the processing circuitry 1208. The software 1210 includes a host application 1212. The host application 1212 may be operable to provide a service to a remote user, such as a UE 1214 connecting via an OTT connection 1216 terminating at the UE 1214 and the host computer 1202. In providing the service to the remote user, the host application 1212 may provide user data which is transmitted using the OTT connection 1216.

[0159] The communication system 1200 further includes a base station 1218 provided in a telecommunication system and comprising hardware 1220 enabling it to communicate with the host computer 1202 and with the UE 1214. The hardware 1220 may include a communication interface 1222 for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system 1200, as well as a radio interface 1224 for setting up and maintaining at least a wireless connection 1226 with the UE 1214 located in a coverage area (not shown in Figure 12) served by the base station 1218. The communication interface 1222 may be configured to facilitate a connection 1228 to the host computer 1202. The connection 1228 may be direct or it may pass through a core network (not shown in Figure 12) of the telecommunication system and / or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, the hardware 1220 of the base station 1218 further includes processing circuitry1230, which may comprise one or more programmable processors, ASICs, FPGAs, or combinations of these (not shown) adapted to execute instructions. The base station 1218 further has software 1232 stored internally or accessible via an external connection.

[0160] The communication system 1200 further includes the UE 1214 already referred to. The UE's 1214 hardware 1234 may include a radio interface 1236 configured to set up and maintain a wireless connection 1226 with a base station serving a coverage area in which the UE 1214 is currently located. The hardware 1234 of the UE 1214 further includes processing circuitry 1238, which may comprise one or more programmable processors, ASICs, FPGAs, or combinations of these (not shown) adapted to execute instructions. The UE 1214 further comprises software 1240, which is stored in or accessible by the UE 1214 and executable by the processing circuitry 1238. The software 1240 includes a client application 1242. The client application 1242 may be operable to provide a service to a human or non-human user via the UE 1214, with the support of the host computer 1202. In the host computer 1202, the executing host application 1212 may communicate with the executing client application 1242 via the OTT connection 1216 terminating at the UE 1214 and the host computer 1202. In providing the service to the user, the client application 1242 may receive request data from the host application 1212 and provide user data in response to the request data. The OTT connection 1216 may transfer both the request data and the user data. The client application 1242 may interact with the user to generate the user data that it provides.

[0161] It is noted that the host computer 1202, the base station 1218, and the UE 1214 illustrated in Figure 12 may be similar or identical to the host computer 1116, one of the base stations 1106A, 1106B, 1106C, and one of the UEs 1112, 1114 of Figure 11, respectively. This is to say, the inner workings of these entities may be as shown in Figure 12 and independently, the surrounding network topology may be that of Figure 11.

[0162] In Figure 12, the OTT connection 1216 has been drawn abstractly to illustrate the communication between the host computer 1202 and the UE 1214 via the base station 1218 without explicit reference to any intermediary devices and the precise routing of messages via these devices. The network infrastructure may determine the routing, which may be configured to hide from the UE 1214 or from the service provideroperating the host computer 1202, or both. While the OTT connection 1216 is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network).

[0163] The wireless connection 1226 between the UE 1214 and the base station 1218 is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the UE 1214 using the OTT connection 1216, in which the wireless connection 1226 forms the last segment. More precisely, the teachings of these embodiments may improve the [INSERT HERE THE APPLICABLE RAN EFFECT: E.G., DATA RATE, LATENCY, POWER CONSUMPTION] and thereby provide benefits such as [INSERT HERE THE APPLICABLE CORRESPONDING EFFECT ON THE OTT SERVICE: E.G., REDUCED USER WAITING TIME, RELAXED RESTRICTION ON FILE SIZE, BETTER RESPONSIVENESS, EXTENDED BATTERY LIFETIME].

[0164] A measurement procedure may be provided for the purpose of monitoring data rate, latency, and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection 1216 between the host computer 1202 and the UE 1214, in response to variations in the measurement results. The measurement procedure and / or the network functionality for reconfiguring the OTT connection 1216 may be implemented in the software 1210 and the hardware 1204 of the host computer 1202 or in the software 1240 and the hardware 1234 of the UE 1214, or both. In some embodiments, sensors (not shown) may be deployed in or in association with communication devices through which the OTT connection 1216 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which the software 1210, 1240 may compute or estimate the monitored quantities. The reconfiguring of the OTT connection 1216 may include message format, retransmission settings, preferred routing, etc.; the reconfiguring need not affect the base station 1218, and it may be unknown or imperceptible to the base station 1218. Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating the host computer's 1202 measurements of throughput, propagation times, latency, and the like. Themeasurements may be implemented in that the software 1210 and 1240 causes messages to be transmitted, in particular empty or 'dummy' messages, using the OTT connection 1216 while it monitors propagation times, errors, etc.

[0165] Figure 13 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station, and a UE which may be those described with reference to Figures 11 and 12. For simplicity of the present disclosure, only drawing references to Figure 13 will be included in this section. In step 1300, the host computer provides user data. In sub-step 1302 (which may be optional) of step 1300, the host computer provides the user data by executing a host application. In step 1304, the host computer initiates a transmission carrying the user data to the UE. In step 1306 (which may be optional), the base station transmits to the UE the user data which was carried in the transmission that the host computer initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In step 1308 (which may also be optional), the UE executes a client application associated with the host application executed by the host computer.

[0166] Figure 14 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station, and a UE which may be those described with reference to Figures 11 and 12. For simplicity of the present disclosure, only drawing references to Figure 14 will be included in this section. In step 1400 of the method, the host computer provides user data. In an optional sub-step (not shown) the host computer provides the user data by executing a host application. In step 1402, the host computer initiates a transmission carrying the user data to the UE. The transmission may pass via the base station, in accordance with the teachings of the embodiments described throughout this disclosure. In step 1404 (which may be optional), the UE receives the user data carried in the transmission.

[0167] Figure 15 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station, and a UE which may be those described with reference to Figures 11 and 12. For simplicity of the present disclosure, only drawing references to Figure 15 will be included in this section. In step 1500 (which may be optional), the UE receives input data provided by the host computer.Additionally or alternatively, in step 1502, the UE provides user data. In sub-step 1504 (which may be optional) of step 1500, the UE provides the user data by executing a client application. In sub-step 1506 (which may be optional) of step 1502, the UE executes a client application which provides the user data in reaction to the received input data provided by the host computer. In providing the user data, the executed client application may further consider user input received from the user. Regardless of the specific manner in which the user data was provided, the UE initiates, in sub-step 1508 (which may be optional), transmission of the user data to the host computer. In step 1510 of the method, the host computer receives the user data transmitted from the UE, in accordance with the teachings of the embodiments described throughout this disclosure.

[0168] Figure 16 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station, and a UE which may be those described with reference to Figures 11 and 12. For simplicity of the present disclosure, only drawing references to Figure 16 will be included in this section. In step 1600 (which may be optional), in accordance with the teachings of the embodiments described throughout this disclosure, the base station receives user data from the UE. In step 1602 (which may be optional), the base station initiates transmission of the received user data to the host computer. In step 1604 (which may be optional), the host computer receives the user data carried in the transmission initiated by the base station.

[0169] Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processors (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and / ordata communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according to one or more embodiments of the present disclosure.

[0170] While processes in the figures may show a particular order of operations performed by certain embodiments of the present disclosure, it should be understood that such order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc.).

[0171] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein.

Claims

Claims1. A method performed by a User Equipment, UE, (602) for obtaining an estimate of a position of the UE (602) in a cellular communications system (600), the method comprising: receiving (704) position assistance information from a Terrestrial Network, TN, node (606) on a TN cell (604); obtaining (706) a position of the UE (602) based on the position assistance information; and performing (708) one or more actions with respect to one or more NonTerrestrial Network, NTN, cells (610), based on the position of the UE (602) obtained based on the position assistance information.

2. The method of claim 1, wherein the one or more actions comprise performing measurements on the one or more NTN cells (610), based on the position of the UE (602) obtained based on the position assistance information.

3. The method of claim 1 or 2, wherein the one or more actions comprise performing uplink synchronization with respect to a NTN cell (610) from among the one or more NTN cells (610), based on the position of the UE (602) obtained based on the position assistance information.

4. The method of any of claims 1 to 3, wherein the position obtained based on the position assistance information is used to perform the one or more actions in place of a position of the UE obtained via a Global Navigation Satellite System, GNSS, receiver.

5. The method of any of claims 1 to 4, wherein receiving (704) the position assistance information comprises receiving broadcast information comprising the position assistance information on the TN cell (604).

6. The method of any of claims 1 to 4, wherein receiving (704) the position assistance information comprises receiving the position assistance information via one or more dedicated messages.

7. The method of any of claims 1 to 6, wherein the UE (602) is located at a position that is served by both the TN cell (604) and at least one of the one or more NTN cells (610).

8. The method of any of claims 1 to 7, wherein the position assistance information comprises position assistance information for the TN cell (604).

9. The method of any of claims 1 to 7, wherein the position assistance information comprises position assistance information for the TN cell (604) and position assistance information for one or more additional TN cells.

10. The method of claim 9, wherein obtaining (706) the position of the UE (602) based on the position assistance information comprises obtaining (706) the position of the UE (602) based on the position assistance information for the TN cell (604) and the position assistance information for one or more additional TN cells.

11. The method of any of claims 1 to 7, wherein the position assistance information comprises a position of an antenna which the TN node (606) uses for downlink transmissions and uplink receptions in the TN cell (604), and obtaining (706) the position of the UE (602) based on the position assistance information comprises using the position of the antenna which the TN node (606) uses for downlink transmissions and uplink receptions in the TN cell (604) as the position of the UE (602).

12. The method of any of claims 1 to 7, wherein: the position assistance information comprises information that provides a mapping between a plurality of Synchronization Signal, SS, I Physical Broadcast Channel, PBCH, Block, SSB, beams and a respectively plurality of geographical coordinates within a coverage are of the TN cell (604); and obtaining (706) the position of the UE (602) based on the position assistance information comprises selecting one of the plurality of geographical coordinates that is mapped to one of the SSB beams as the position of the UE (602).

13. The method of claim 12, wherein the selected one of the plurality of geographical coordinates is one of the plurality of geographical coordinates that is mapped to one of the plurality of SSB beams that satisfies a predefined criterion.

14. The method of claim 13, wherein the predefined criterion is a criterion that the one of the plurality of SSB beams is the one having a highest Reference Signal Received Power, RSRP, at the UE (602).

15. The method of any of claims 1 to 7, wherein: the position assistance information comprises a position of an antenna which the TN node (606) uses for downlink transmissions and uplink receptions in the TN cell (604) that is common for a plurality of Synchronization Signal, SS, I Physical Broadcast Channel, PBCH, Block, SSB, beams and information that indicates a plurality of beam directions for the plurality of SSB beams, respectively; and obtaining (706) the position of the UE (602) based on the position assistance information comprises computing the position of the UE (602) based on the position of the antenna, one of the plurality of beam directions indicated for one of the plurality of SSB beams in which the UE (602) is located, and a current Timing Advance, TA, of the UE (602) used for uplink transmissions in the TN cell (604).

16. The method of any of claims 1 to 7, wherein:• the position assistance information comprises: o a position of an antenna which the TN node (606) uses for downlink transmissions and uplink receptions in the TN cell (604) that is common for a plurality of Synchronization Signal, SS, I Physical Broadcast Channel, PBCH, Block, SSB, beams; o information that indicates a plurality of beam directions for the plurality of SSB beams, respectively; and o a round-trip time, RTT, between the antenna and a defined uplink time synchronization reference point for the TN cell (604); and• obtaining (706) the position of the UE (602) based on the position assistance information comprises computing the position of the UE (602) based on the position of the antenna, one of the plurality of beam directions indicated for oneof the plurality of SSB beams in which the UE (602) is located, a current Timing Advance, TA, of the UE (602) used for uplink transmissions in the TN cell (604), and the RTT between the antenna and the defined uplink time synchronization reference point for the TN cell (604).

17. The method of any of claims 1 to 7, wherein:• the position assistance information comprises: o a position of an antenna which the TN node (606) uses for downlink transmissions and uplink receptions in the TN cell (604) that is common for a plurality of Synchronization Signal, SS, I Physical Broadcast Channel, PBCH, Block, SSB, beams; o information that indicates a beam direction for at least one of the plurality of SSB beams; and• obtaining (706) the position of the UE (602) based on the position assistance information comprises computing the position of the UE (602) based on: o the position of the antenna; o a beam direction of one of the plurality of SSB beams in which the UE (602) is located as indicated by or derived from the information that indicates the beam direction for the at least one of the plurality of SSB beams; and o a current Timing Advance, TA, of the UE (602) used for uplink transmissions in the TN cell (604).

18. The method of claim 17, wherein the UE (602) derives the beam direction of the one of the plurality of SSB beams in which the UE (602) is located based on the information that indicates the beam direction for the at least one of the plurality of SSB beams and a known number of SSB beams used in the TN cell (604).

19. The method of claim 17 or 18, wherein the at least one of the plurality of SSB beams for which the position information comprises the information that indicates the beam direction comprises a single SSB beam from among the plurality of SSB beams.

20. The method of claim 17 or 18, wherein the at least one of the plurality of SSB beams for which the position information comprises the information that indicates the beam direction comprises two SSB beams from among the plurality of SSB beams that are correspond to edge beams of a corresponding sector antenna of the TN node (606).

21. The method of any of claims 1 to 7, wherein: the position assistance information comprises information that indicates a plurality of positions of a plurality of Synchronization Signal, SS, / Physical Broadcast Channel, PBCH, Block, SSB, beams, respectively; and obtaining (706) the position of the UE (602) based on the position assistance information comprises using one of the plurality of positions indicated for one of the plurality of SSB beams in which the UE (602) is located as the position of the UE (602).

22. The method of claim 21, wherein the information that indicates the plurality of positions of the plurality of SSB beams, respectively, comprises, for each SSB beam of the plurality of SSB beams, geographic coordinates that indicate the position of the SSB beam.

23. The method of any of claims 1 to 7, wherein:• the position assistance information comprises: o geographical coordinates of an antenna which the TN node (606) uses for downlink transmissions and uplink receptions in the TN cell (604) that is common for a plurality of Synchronization Signal, SS, I Physical Broadcast Channel, PBCH, Block, SSB, beams; and o geographical coordinates for at least one of the plurality of SSB beams; and• obtaining (706) the position of the UE (602) based on the position assistance information comprises deriving the position of one of the plurality of SSB beams in which the UE (602) is located from the geographical coordinates of the antenna and the geographical coordinates for the at least one of the plurality of SSB beams.

24. The method of any of claims 1 to 23, wherein the UE (602) is served by the TN cell (604).

25. The method of any of claims 1 to 23, wherein the UE (602) is served by one of the one or more NTN cells (610).

26. The method of any of claims 1 to 25, wherein the UE (602) performs the method while in a low activity radio resource control state.

27. The method of any of claims 1 to 25, wherein the UE (602) performs the method while in a radio resource control connected state.

28. A User Equipment, UE, (602) for obtaining an estimate of a position of the UE (602) in a cellular communications system (600), the UE adapted to: receive (704) position assistance information from a Terrestrial Network, TN, node (606) on a TN cell (604); obtain (706) a position of the UE (602) based on the position assistance information; and perform (708) one or more actions with respect to one or more Non-Terrestrial Network, NTN, cells (610), based on the position of the UE (602) obtained based on the position assistance information.

29. The UE of claim 28 further adapted to perform the method of any of claims 2 to 27.

30. A User Equipment, UE, (602; 1000) for obtaining an estimate of a position of the UE (602) in a cellular communications system (600), the UE (602; 1000) comprising: one or more transmitters (1008); one or more receivers (1010); and processing circuitry (1002) associated with the one or more transmitters (1008) and the one or more receivers (1010), the processing circuitry (1002) configured to cause the UE (602; 1000) to:receive (704) position assistance information from a Terrestrial Network, TN, node (606) on a TN cell (604); obtain (706) a position of the UE (602; 1000) based on the position assistance information; and perform (708) one or more actions with respect to one or more NonTerrestrial Network, NTN, cells (610), based on the position of the UE (602; 1000) obtained based on the position assistance information.

31. The UE (602; 1000) of claim 30, wherein the processing circuitry (1002) is further configured to cause the UE (602; 1000) to perform the method of any of claims 2 to 27.

32. A computer program comprising instructions which, when executed on at least one processor, cause the processor to carry out the method according to any of claims 1 to 27.

33. A carrier containing the computer program of claim 32, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium.

34. A non-transitory computer-readable medium comprising instructions executable by processing circuitry of a User Equipment, UE, whereby the UE is operable to: receive (704) position assistance information from a Terrestrial Network, TN, node (606) on a TN cell (604); obtain (706) a position of the UE (602) based on the position assistance information; and perform (708) one or more actions with respect to one or more Non-Terrestrial Network, NTN, cells (610), based on the position of the UE (602) obtained based on the position assistance information.

35. A method performed by a Terrestrial Network, TN, node (606), comprising:providing (704) position assistance information to a User Equipment, UE, (602) on a TN cell (604); wherein the position assistance information comprises information that enables the UE (602) to select or derive a position of the UE (602).

36. The method of claim 35, wherein providing (704) the position assistance information to the UE (602) comprises transmitting broadcast information comprising the position assistance information on the TN cell (604).

37. The method of claim 35, wherein providing (704) the position assistance information comprises transmitting the position assistance information to the UE (602) via one or more dedicated messages.

38. The method of any of claims 35 to 37, wherein the UE (602) is located at a position that is served by both the TN cell (604) and at least one Non-Terrestrial Network, NTN, cell (610).

39. The method of any of claims 35 to 38, wherein the position assistance information comprises position assistance information for the TN cell (604).

40. The method of any of claims 35 to 38, wherein the position assistance information comprises position assistance information for the TN cell (604) and position assistance information for one or more additional TN cells.

41. The method of any of claims 35 to 40, wherein the position assistance information comprises a position of an antenna which the TN node (606) uses for downlink transmissions and uplink receptions in the TN cell (604).

42. The method of any of claims 35 to 40, wherein the position assistance information comprises information that provides a mapping between a plurality of Synchronization Signal, SS, I Physical Broadcast Channel, PBCH, Block, SSB, beams and a respectively plurality of geographical coordinates within a coverage are of the TN cell (604).

43. The method of any of claims 35 to 40, wherein the position assistance information comprises a position of an antenna which the TN node (606) uses for downlink transmissions and uplink receptions in the TN cell (604) that is common for a plurality of Synchronization Signal, SS, I Physical Broadcast Channel, PBCH, Block, SSB, beams and information that indicates a plurality of beam directions for the plurality of SSB beams, respectively.

44. The method of any of claims 35 to 40, wherein the position assistance information comprises: a position of an antenna which the TN node (606) uses for downlink transmissions and uplink receptions in the TN cell (604) that is common for a plurality of Synchronization Signal, SS, I Physical Broadcast Channel, PBCH, Block, SSB, beams; information that indicates a plurality of beam directions for the plurality of SSB beams, respectively; and a round-trip time, RTT, between the antenna and a defined uplink time synchronization reference point for the TN cell (604).

45. The method of any of claims 35 to 40, wherein the position assistance information comprises: a position of an antenna which the TN node (606) uses for downlink transmissions and uplink receptions in the TN cell (604) that is common for a plurality of Synchronization Signal, SS, I Physical Broadcast Channel, PBCH, Block, SSB, beams; and information that indicates a beam direction for at least one of the plurality of SSB beams.

46. The method of claim 45, wherein the at least one of the plurality of SSB beams for which the position information comprises the information that indicates the beam direction comprises a single SSB beam from among the plurality of SSB beams.

47. The method of claim 45, wherein the at least one of the plurality of SSB beams for which the position information comprises the information that indicates the beamdirection comprises two SSB beams from among the plurality of SSB beams that correspond to edge beams of a corresponding sector antenna of the TN node (606).

48. The method of any of claims 35 to 40, wherein the position assistance information comprises information that indicates a plurality of positions of a plurality of Synchronization Signal, SS, I Physical Broadcast Channel, PBCH, Block, SSB, beams, respectively.

49. The method of claim 48, wherein the information that indicates the plurality of positions of the plurality of SSB beams, respectively, comprises, for each SSB beam of the plurality of SSB beams, geographic coordinates that indicate the position of the SSB beam.

50. The method of any of claims 35 to 40, wherein the position assistance information comprises: geographical coordinates of an antenna which the TN node (606) uses for downlink transmissions and uplink receptions in the TN cell (604) that is common for a plurality of Synchronization Signal, SS, I Physical Broadcast Channel, PBCH, Block, SSB, beams; and geographical coordinates for at least one of the plurality of SSB beams.

51. A Terrestrial Network, TN, node (606) adapted to: provide (704) position assistance information to a User Equipment, UE, (602) on a TN cell (604); wherein the position assistance information comprises information that enables the UE (602) to select or derive a position of the UE (602).

52. The TN node (606) of claim 51 further adapted to perform the method of any of claims 36 to 50.

53. A Terrestrial Network, TN, node (606) comprising processing circuitry configured to cause the TN node (606) to:provide (704) position assistance information to a User Equipment, UE, (602) on a TN cell (604); wherein the position assistance information comprises information that enables the UE (602) to select or derive a position of the UE (602).

54. The TN node (606) of claim 53, wherein the processing circuitry is further configured to cause the TN node (606) to perform the method of any of claims 36 to 50.

55. A computer program comprising instructions which, when executed on at least one processor, cause the processor to carry out the method according to any of claims 35 to 50.

56. A carrier containing the computer program of claim 55, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium.

57. A non-transitory computer-readable medium comprising instructions executable by processing circuitry of a Terrestrial Network, TN, node, whereby the TN node is operable to: provide (704) position assistance information to a User Equipment, UE, (602) on a TN cell (604); wherein the position assistance information comprises information that enables the UE (602) to select or derive a position of the UE (602).

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